I use fossify phone too and that happens whenever I hit the home button during a call. The phone app doesn’t show up in the notification bar nor in the task list. Pretty annoying. I’ve tried some alternatives but from what I can tell they come with their own, even more glaring issues.

I just keep a Windows partition on my PCs for those few occasions where I need it. Usually about a tenth of the drive. For most stuff you can mess around with a vm or wine too but this way is easier imo. And realistically Windows 10 will be fine to use for the forseeable future. It’s still possible to use XP securely even today.