Reproducible in versions 1.12.2, 1.18.2, 1.20.1, and 1.21.9-rc1. It appears that when pathfinding is insufficient, creepers ignore cats and focus solely on attacking the player.
Unable to reproduce; the hitbox of the stair item entity appears completely normal. Additionally, it is noted that you are using a resource pack, which may be the cause of the issue.
Cannot reproduce the issue; copper blocks oxidize normally. It is suggested to attempt using the /gamerule randomTickSpeed 3000
command to accelerate the process for verification.
Unable to reproduce. You may need to wait for a longer duration.