Around 2021, I regularly ran into this problem with the Firefox snap. It had various runtime issues, so I preferred the traditional deb package. I’d uninstall the snap then install the deb. Then, some days later, I’d find the snap was somehow installed again. This happened a few times before I realized that the deb was just installing the snap. Imo, that’s not a good design. Debs should be debs and snaps should be snaps.

Anyhow, I use Arch now, btw. Much more consistent experience.