I get the following error:
FATAL:setuid_sandbox_host.cc(158)] The SUID sandbox helper binary was found, but is not configured correctly. Rather than run without sandboxing I'm aborting now. You need to make sure that /tmp/user/1000/.mount_mapillu0GmM8/chrome-sandbox is owned by root and has mode 4755.
This I was able to solve with
./mapillary-uploader-4.4.1.AppImage --no-sandbox
Then it works, but the very useful drag&drop seems still broken on Kubuntu 24.04 with Plasma 5 on wayland. My suspicion is now that this is a general problem with browsers on that platform.
Maybe I just need to wait for Kubuntu 24.10 which comes out in October with Plasma 6 and should have multiple bugfixes in that direction, e.g.:
https://bugs.kde.org/show_bug.cgi?id=484018
https://bugs.kde.org/show_bug.cgi?id=482142
https://bugs.kde.org/show_bug.cgi?id=469644