I haven’t used Tuxedo, but on apt-based distros it’s pretty common for an auto-update daemon of some kind to run in the background on startup to either download updates, or at least download package metadata so some UI component can start nagging you to install the updates that are available.
If you wait a few minutes, the download should complete and you can do what you want. You can probably get away with killing it, especially if you use a gentle signal like HUP. I wouldn’t risk it though… if you corrupt your package metadata or worse… and actual important package… it can be a significant hassle to clean up the mess. And the cost of waiting 30s-5m and trying again is so low it’s hard to beat that as an approach.
If its happening a ton you can probably find and disable the auto-update thing but I don’t know what it would be on Tuxedo.