Trying to upload a 2mb image gives the displayed error message (Max size 4Mb). Not sure whether this is part of a larger Discourse issue, because there are a lot of similar posts from forum owners relating to image size, but based on this thread, maybe there are some options you can tweak to fix this on your side? Other posts highlight issues with the automatic resize options.
The discourse devs are not that helpful on this topic, suggesting things like “Change the image to a jpg first” which is a terrible suggestion when the forum software allows to paste PrtScn screenshots directly into the post box.
I understand this will likely be a busy time, but fine tuning the forums will help a lot in the not too distant future.