I don’t think there are hard-and-fast rules that will work here. Be polite and considerate. Be mindful that mentioning someone pings them and takes a small bit of their time and attention. Use it only if you think they want to / should be made aware of something. Yes, people can turn off all notification, but that’s effectively a total self-removal from the community and they may want to remain somewhat but minimally involved.
You can direct message people if need be, but please be even more mindful of doing that. When someone direct messages you, you are then giving time just to that one person instead of to anyone who might ever care to know about the topic that’s being discussed in a public conversation.