Crash log:
https://pastebin.com/ViHfef4H
Mods used:

the pastebin is private

the pastebin is private

Sorry for delay. I think the pastebin was awaiting manual review for some reason. Original link appears to work now in incognito mode.

I am also getting crashes that I have isolated to the Capes mod. It seems to be worse when there are a lot of players in the area. If there are too many players sometimes it crashes instantly. Disabling capes I have zero issues in those situations.

Sorry it took a while for me to come back to this, have you tried the 1.16.5 version of the mod instead of the 1.16.1 one? I would also like to know what provider (optifine, labymod, etc) you are using when it crashes.