After around 6 years, I finally get an ANSWER!!!
So, tags are only acting as a warning for "SEX CONTENT".
Lesbian/yuri is considered a "SEX FETISH", rather than themes or character settings, right?
There was a debate some months ago when the devteam was reworking the tags.
A lot of people wanted a "female protagonist" tag to be added, so we could make the difference between games with some lesbian scenes, and game with a lesbian route.
Unfortunately, such a tag wasn't added.
And while it could help a lot, what some people actually consider lesbian content is up to them, as you can see in the most recent debate.
For example, some people consider futaxfemale to be lesbian, personally, I don't. For me, lesbian means no dick involved.
On the other hand, some games that offer a lesbian path, or at least explore W/W relationship can be considered lesbian, such as "abnormal", which isn't considered by most here as a lesbian protagonist game, because the main character is mostly curious instead of pure lesbian (though any thought or interaction with males genitals can be easily avoided).
While we are on the matter of personal taste, someone suggested above using the lgbt tag on steam.
Personally, I don't like it. I mostly prefer games that focus on the characters and relationships (yuri), from personal experience, a lot of game being part of lgbt campaigns you can find on itch.io packs, etc... focus more on the external eye and what it means to be gay than the relationship proper.
To give a good example, take the legend of Korra comics.
I'll be honest, I only began to gain interest in the Avatar franchise when I learnt the main character in legend of Korra was a lesbian.
And, huh... was extremely disappointed with the show on that regard (still an excellent show though). Seriously, she's in an hetero relationship most of the show, she only talks to the other woman like 2 times, and at the end of the very last episode, they hold hand and go through a portal.
The lgbt community went apeshit with "LOOK FINALLY A LESBIAN HEROINE!!!!!" The entire preface of the first comic talks just about that. And it is an important part of said comic, but the way it is approached is "society might not be ready for such a relationship, be careful of what others might think of it", counterbalanced by "I'm a strong woman, i don't care about what other think", etc...
I don't give two f* about all that crap, just focus on the relationship. Yeah, I know, real life is full of hardship, for everyone really.
If I play games, watch tv shows and read comics/manga/BD, whatever, it's to not have to deal with this. I just want fiction with sweet women relationships.
Which bring us back to topic, what I want in lesbian protagonist games are games where the female MC is mostly in a relationship with other female characters. If we have a "woman eye" style of writing, all the better. But as a man myself, I know it's hard to have such an eye unless you manage to get a lesbian, or even a straight woman in your team to help with the writing, and considering most AVN dev team are made of a single dev... you know where I'm going with this.