It should be on by default. Any time a notification pops up at the top of your screen, there should be a little clock icon that snoozes (default is 1hr, but there's a drop down)
I'm on base android. I don't know if that makes a difference.
it may also look like the YouTube bell, not every app supports it though, usually it's only apps that give you an ability to do something, but it's not accessed by hold pressing it, you click the little arrow to the right of the notice and then it appears
Make time to check them if it's important or be clear that it's a dead communication line if you can't maintain it. As a fellow ADHDer I've had to back out of a few different platforms because I simply can't allow myself to engage with them - if someone @s me on Facebook I'll see it in six months to a decade... I do try and make sure my contacts all have good lines to me if they need to reach out, though.