Oof, free legit ones (not particularly manga) i can think of are webtoons, webcomics, tapas and lezhin i think. Kinda hard for me to find legit and free mangas
As far as I know mangadex is the only major aggregator considered "legit", in the sense that it will refuse scans of official translations, take down chapters if the scanlators request it, and often it is the scanlators uploading the chapters themselves directly to it. Of course a truly legit site would be one with actual license to every manga featured, which kinda rules out aggregators in general.
mangaplus.shueisha.co.jp legit manga site under the direct control of SHUEISHA, a Japanese publisher that has been creating manga directly with the artists. Reading Manga through this official service - “MANGA Plus by SHUEISHA” - will also help support manga artists produce sequels and new worksnglish and spanish
Tappytoon Tapas Manta Pocket Comics Lezhin WebComics (by WebComics Holdings HK) Webnovel (has comics too)
Another place I recommend visiting is actually people's local libraries. A lot of librarians would actually be willing to order certain manga if enough people express interest in it, and it's a way I've experienced a lot of manga legally and for free. I even got them to stock a light novel I was interested in, when I told the Adult Librarian about it (A Kid from the Last Dungeon Boonies Goes to Starter Town was the one I got stocked).
Lezhin is great as far as webtoons are concerned. I agree with anokatax that libraries are a phenomenal option, though.
Problems persist in finding Legit Japanese manga in India... Lisence restrictions ...so, I've stopped looking.
There is also MangaDex? It was shut down till a while ago, cuz of a hacker attack, but its up and running again, with some new things, Not sure it's legit, but translators usually post the translated chapters there
If one is not sure if it is a aggregator site just read it at the translator page and mangaplus shueisha is pretty nice and clean (ad wise)
Alpha Manga - www(.)alpha-manga(.)com/ Comikey - comikey(.)com/ Mangaflip - mangaflip(.)com/ The 3 publish/translate manga officially