My site is 25 years old this year. It has been on xenforo for the past 12 years; was vbulletin and others previously. I've recently eradicated all references to "online now" and "last seen viewing" details, etc. I do keep the green dot in the user's avatar so folks viewing or using a thread have a frame of reference. Also, Member profiles and lists are only visible when logged in (not for guests). I don't believe users want this depth of "online" visibility in post-Facebook / social platform world. Let the posts and actions (e.g., likes, as shows up in Latest Activity) speak for themselves.
Of note: X doesn't have any features which tells you if a user is online, or what they were last doing, outside of their public actions themselves (e.g., go to a profile and see what they most recently posted or re-posted). They've even removed visibility of "likes," outside of the content owner.