Finding Zettai Ryouiki R! was pretty hard and the only site I could find lists it as a label not a magazine. Furthermore Zettai Ryouiki R! has many series falsely tagged as josei, while they mostly deal in yaoi and adult manga. Please correct me if I'm wrong.

Screamo, WWWavecomics and Mobile Media Research's Ero Mangatou also have many adult manga tagged as seinen or josei.

This is the only link I could find that lists series from it https://manba.co.jp/labels/1000. A japanese manga store I suppose.

Adult manga can be josei or seinen -- nothing about either of these labels precludes other genre tags by definition, except for obvious contradictions like shojo and shounen. You normally wouldn't see 'josei' or 'seinen' and 'yaoi' in the same grouping because magazines will often label themselves as one or the other to target their key demographics, but I don't think it's wrong by definition. Something can be josei (targeting older women) and yaoi (which is the content) in theory. Similarly porn magazines aimed at women and men are likely to be sub-divded, just due to what each of those demos might want, so 'josei' and 'adult' could very well be something they label. I guess it would be a matter of how they officially brand themselves because there aren't any real rules to this beyond what the magazine it was published in.

I was able to find that as a label (I think magazines and imprints and labels are used interchangeably) by searching it up on Amazon (in Japanese: 絶対領域R!) with the publisher being Screamo (スクリーモ).

Not sure if this link will work but as you said, there are a lot of Adult manga but they look mainly non-yaoi: https://www.amazon.co.jp/s?k=%E7%B5%B6%E5%AF%BE%E9%A0%98%E5%9F%9FR%21&rh=n%3A2293143051&ref=nb_sb_noss

Here are posts tagged on the Screamo website (I just copied the link from Google because I have never seen a top level domain being .ooo, but according to their Twitter [https://twitter.com/TLscr_Yuwae], this is the official website): https://screamo.ooo/tag/%E7%B5%B6%E5%AF%BE%E9%A0%98%E5%9F%9Fr%EF%BC%81 but if you wanna look on twitter, this tweet from them advertising a story in the magazine: https://twitter.com/TLscr_Yuwae/status/1140785951318261760 - based on the date, it's announcing the book volume 2 of Yubisaki kara Honki no Netsujou - Charao Shouboushi wa Massugu na Me de Watashi o Daita.

http://i.imgur.com/LxhWm.jpg (will reformat this some day…)

To clarify I meant adult as in pornographic. I'm not saying a amagzine can't have an age demographic and publish yaoi, just that in the case of Zettai Ryouiki R! the covers show either yaoi or erotic pictures/names. The amazon link you provided shows me only volumes with the magazine in question included in parentheses next to the name, but not in the description where Screamo is listed as the publisher. This doesn't clarify the relation of Zettai Ryouiki R! to the volumes.
I've looked for dlsite and found this https://www.amazon.co.jp/-/en/%E8%96%BA%E5%B1%8B%E6%9C%AC%E8%88%97-ebook/dp/B08ZY46ZBY. DLManiax in parentheses next to the name with no further information besides the publisher being DLcomics. A quick search led me to cmoa found here https://www.cmoa.jp/magazine/11202/ that lists DLManiax as a label.
This just got more confusing. On the bottom of Screamo's website is a link to WWWave Corporation and above that on the right there is a link to wwwave comics. According to this https://www.mangaupdates.com/publisher/z2kmyad/wwwave-corporation the corporation owns all of these product; with Screamo etc. acting as brands but according to amazon at least also as publishers. Now wwwave comics has clickable pictures that look like magazines.But they only publish books. Furthermore the names appear on the right side as labels. Meaning wwwavecomics publishes only books under different labels. This leads me to the conclusion that Zettai Ryouiki R! is indeed a label by the brand/publisher Screamo belonging to WWWave Corporation.
As the word label is mentioned with studio73 in the mangaupdates link I provided. What does this site do with labels?

Adult manga tend to have smutty covers. 😅

That cmoa link shows DLManiax under "雑誌・レーベル" which is "magazine/label." If you search up, Zettai Ryouiki R! it also shows up in the same place, under magazine/label (example: https://www.cmoa.jp/title/175998/) with Screamo as publisher (出版社). For contrast, here is Naruto, that has Weekly Shounen Jump/Jump Comic Digital in the same place under "magazine/label": https://www.cmoa.jp/title/46812/. Just wanted to add it since that one I know this is a physical publication & magazine that Naruto was published in.

In this context, it appears that Zettai Ryouiki R! is a label or imprint used by Screamo, and it may also represent a specific online magazine or collection of manga series produced by them. You're right in that it isn't clear, but I think the fact that the two terms are grouped together for organizational purposes signals that, in the context of online publishing (which is what they seem to only offer), these two are interchangeable for the purpose of categorizing titles by genre or target demographic. Again, you're right - by definition, they are two different things (a magazine being a collated work rather than a simple grouping) but their general categorical function is the same and they should be organized the same way, in my opinion, in that a label would go where the magazine information would go, in a similar fashion to what cmoa is doing to categorize.

wwwave has their fingers in many pots - they are essentially the facilitators of these things and they also own Coolmic and ComicFesta, it seems like, along with a host of other things. studio73 is a production studio for webtoons - labels produced by this production studio include libish for men or flaoto for women, as it states on the MU page and also here on their website: https://wwwave.jp/2022/04/05/%E3%80%8Cstudio73%E3%80%8D%E3%81%AB%E3%81%A6webtoon%E3%83%AC%E3%83%BC%E3%83%99%E3%83%AB%E3%82%92%E7%AB%8B%E3%81%A1%E4%B8%8A%E3%81%92%E3%80%81%E6%BC%AB%E7%94%BB%E5%AE%B6%E5%8E%9F%E4%BD%9C%E3%81%AE/. The production studio manages and recruits artists and authors for works in these two labels. libish and flaoto would be treated in the same way as Zettai Ryouiki R! or DLManiax. studio73 would be treated the same way as Screamo, I would imagine. At this point, we're getting into the business side of publishing.

I agree with your conclusion: "This leads me to the conclusion that Zettai Ryouiki R! is indeed a label by the brand/publisher Screamo belonging to WWWave Corporation." But I guess what I am confused about is, what is your definition of a magazine and what do you propose MU do with labels vs magazines? Is there a genuine difference when it comes to webtoons and online-only comics between a magazine and a label or do they serve the same function (which is what I feel at this point)? Is there an importance to this distinction that warrants a change? The label that says "Magazine" could simply be updated to "Magazine/Label," I guess.

http://i.imgur.com/LxhWm.jpg (will reformat this some day…)