filesystem error: status: Permission denied [mkvmerge]

I've seen some users reporting that MKVToolNix GUI crashes when starting:

terminate called after throwing an instance of 'std::filesystem::__cxx11::filesystem_error'
  what():  filesystem error: status: Permission denied [mkvmerge]

Do you have any pointer about where this error could come from ?

So far, reports are from users running MKVToolNix in Docker, on Synology NASes. The issue seems to have appeared in v73 (v72 works fine).