Do you need a stickied notification? Not sure if that’s enough for what you’re looking for, but a reminder/task app with reoccurring options and a non-dismissable feature might work. Ruppu, Taskito, and I think Microsoft’s To Do might also have this option.
Repeating reminder: DO NOT CALL between 10pm-2am would work, for example.
PiP won’t work with two media apps? Ugh, I was hoping I could watch two sports games concurrently! Especially during times like now and October, where you have playoff games of one sport and the regular season swing of your favorite teams in the other. I can do this with my Tab S8! If only it could work natively.