I mentioned this in a post here several weeks back, but couldn’t remember which app installed from a .deb package had displayed an ad when I first started it.
Looking for a new to-do app today I came across it again and, as requested, am sharing this since I can now name the app (and now I’m uninstalling it again).
The app is WeekToDo. On the first start it flashed a brief banner for a different app called “SnapClear” - apparently an AI powered image cropping app that is also listed as one of WeekToDo’s sponsors, on the WeekToDo website. I started it again to see if it would continue to display ads but on the second start it did not. So I can’t say if it would continue to do so in the future as I won’t be using it.
[Edit: missed a letter]
Deb packages can be built by anyone, including proprietary software makers. Installing .deb files downloaded from random web sites is like running .exe files downloaded from random web sites. Not safe or (as you discovered) ad-free.
If you want to avoid ads and malware, I suggest installing only from a trustworthy distro’s software repository, using its built-in package manager.