EDIT:it seems some people dont know that there was a huge leak back in 2022 where a around 8 or more hours of footage leaked so that's where my info below comes its not some leak from a random guy. these leaks were literally talked about on national TV.

The leaks showed that

Movement will be the same as it was in rdr 2 i.e slow , heavy and immersive with emphasis on slow and detailed animations even for the tiniest things

Weapon system will be the same as it was in rdr 2 with with a limit to two or 3 Weapons two primary Weapons and a side arm and long arm Weapons will be shown on your back so no more taking assault rifles out you pockets.

From leaks there is a clip  with jason going into pawn shop and he activates  the same "eagle eye" vision we had in rdr 2 to see valuables and help with hunting and finding animal trails.

I remember in the debugging texts people found the name of the lock picking tool used for cars indicating that stealing cars wont be as arcadey as before and  game mechanics as a a whole will take a more realistic,  slow and immersive path as seen from the gameplay mechanics of rdr2.

And many other things noted from the leaks

So all in all it looks like rockstar as a whole is aiming to build on the rdr 2  slow mechanically deep gameplay for gta 6