I would say 99.9% of people are still on Reddit. I mainly use Lemmy to get the bigger news stuff and the gaming community is pretty active here too. Also I use Lemmy on mobile only really since the Reddit app is still terrible.
If I want to read about one of my other interests I’ll go to the specific subreddit on my desktop browser and use old Reddit but with no account since I deleted mine a few months ago. Sometimes I’ll post or comment on one of those smaller communities here but I don’t want to be someone who posts tons of things to a community. Too much work for me.
Hopefully the user base and engagement will grow over the next few years. Welcome to being an early adopter!