[spflmf]

spflmf - I set up Ubuntu Studio 24.10, then ran sudo apt install ./MobileSheetsCompanion.deb, and it installed and ran just fine. So I'm not seeing any issue. I don't know what package installer you were trying to use.

Thanks for investigating Mike, I was using the default app associated with deb files, I.e. downloaded using chrome and then clicked the open file pop-up. This launches an app called qapt-deb-installer which reports the error,  even if launched from cmdline using sudo.

Using sudo apt install, or sudo dpkg -i works perfectly. 

Thanks again for investigating and apologies for the extra work it caused.
Steve