If you've participated or been tagged in a discussion thread but you don't want to take part or receive notifications about it any more, you can remove yourself from the discussion by using the "mute conversation" feature:
️ https://fedi.tips/muting-conversation-threads-in-mastodon
After you've done this, you won't get any more notifications about the thread.
Note that you need to go to your *notifications* to find the option to mute the conversation. This option may not be available in the thread itself.