The uninstalling issue almost certainly isn’t hardware related, Ubuntu’s app store is just a pile of hot garbage. Stuff like that happens all the time, or at least that was my experience years ago when I used Ubuntu, one of the (many) reasons I no longer recommend Ubuntu to new users.
As for the Steam issues, it’s probably a mix of software and hardware issues. It seems there are some permissions issues (likely caused by snap), but it also seems like there are GPU driver issues. What GPU do you have? If you have an Nvidia card, have you installed their drivers? There is also a very real possibility that your card is so old that DayZ is no longer compatible with it (which may be the case given that it wasn’t working in Windows, but to be fair Windows 7 is incredibly out of date and doesn’t receive updates so it could have also been a software/driver issue there).