Is there any way to find out if I've been blocked from a community?

if you're not community banned you might still be instance banned on the community instance, which wouldn't show up in your local instances modlog if the ban happened on a <0.19.4 instance. if the methods pointed out by other comments here fail I suggest you visit the instance of the community and check the site modlog there, searching for your user.

i suspect you're referring to your post to a lemmy.ml community and you have indeed been instance banned there for a limited amount of time.