My friends know I have ADHD and they understand, that's why they're my friends.
If they're going through serious life shit and I'm unresponsive (which I specifically avoid), they'll call or knock on my door.
It's really nice having friends as an adult because you 100% choose each other instead of being forced together because of school/whatever giving you limited options.
I don't open text messages that I need to reply to. I just read them from my notifications and keep them there so that it never goes away and I can't forget about it
I don't have ADHD but I did do it to a friend who sent me way too many messages and links to keep up with. I just started dreading opening the chat, so I stopped doing it.
They eventually caught on and said they wanted to reconnect, so I apologized and came clean. It's been good for years now and I learned from it.
It's gotten to the point where I'm better at remembering who to get back to—and on which platform/medium—than I am at remembering my mental shopping list...