About that rumor, here's what it says:
All fighters from Ultimate return, with some modifications. Link now has some of his abilities from Tears of the Kingdom, Samus has the Dash from Metroid Dread, and Cloud's moveset is modified to represent the recent remakes. In terms of designs, DK is now based on the movie version (which given what we've seen of the new Mario Kart game wouldn't be surprising), Ganondorf now uses his TOTK design, Ryu and Ken now use their SF6 designs, and Bayonetta now uses her Bayonetta 3 design.
The stage roster is severely cut down, and there are now only 50-55 stages.
Art style is mostly the same as Ultimate, but with improved lighting and more expressive facial expressions.
Trophies will make their return after being absent from Ultimate.
Adventure Mode has lots of cutscenes like Brawl, but plays similarly to WOL with the World Map and Spirit fights.
The newcomers in the base roster are Waluigi, Toon Zelda, Noah and Mio, Armarouge/Ceruledge (apparently they're gonna be another transformation fighter like the Aegis), and Sol Badguy. Paper Mario is gonna be added in a similar way to Piranha Plant. They also listed Crash Bandicoot's name, but it's crossed out.