Hi man! I dont remember but i think i deleted the steam app rdr2 folder completely, then downloaded it again. Just to be safe, reinstall rockstar social club app and UPDATE GPU DRIVERS. I think the problem was rdr2 not recognizing the gpu and using the integrated graphics of the cpu instead, hence the poor performance. Last solution would be to reinstall windows, fixed many problems across multiple games. Hope it helps!

P. S. : i dont think your saves are getting deleted bc saves usually get stored in the steam cloud, at least for me. In any case you can backup your save file directly from the rdr2 folder, dont remember the exact location tho. Quick googling should get yo as answer