Hey Jeff! Thank you for your reply, it led me to the fix :). Here’s the issue and solution:
I am running Unreal from an external SSD formatted as ExFAT, and my system HD is APFS. It appears that downloading and unzipping (fmodstudio20207ue4.26mac from the downloads page) created those ._ meta files, but they can’t be seen in Finder (even as hidden).
Solution: I ran the command dot_clean /Volumes/SSK\ Storage in Terminal (after granting full access) and that cleans up those files. After doing that, the build completed successfully.
Thank you so much, I was very stuck! I hadn’t considered it to be related to that because my other plugins were working, and I hadn’t run into any issues before trying to package the game. Cheers!