I had the same issue with Debian 10 today.
Error message read: [15783:1020/171730.403455: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/.mount_Obsidi2tjJk5/chrome-sandbox is owned by root and has mode 4755.
I verified the setting on chrome-sandbox, 4755 and the --appimage-extract failed, invoking components but no app.
Solution: Try /.Obsidian-0.9.4.AppImage --no-sandbox
Worked for me.
Maintainers: I’m guessing its the invocation of chrome-sandbox and not its permissions that is the source of failure here. The interface appears to be working properly, so far as I can tell.