The active sort does a good job of bumping new activity on older posts (limited to 2 days) back to the top. There’s also a New Comments sort that doesn’t have that 2-day limit (making it basically a forum sort), but I don’t know how many people use it.
Not sure what else we could do tho, the main problem is probably just the smaller number of users. Which needs to be tackled by convincing reddit communities and their mods to move them over to some lemmy instance.