I restarted Sync on my iMac and got this:
I also looked on my laptop (MBP) and while not quite as bad it is almost as bad. It too is on BigSur. I had a friend who was _not_ on BigSur look to see how much memory he was using and it was only at 550mb. Not sure how the "number of shares" effects memory but I do have a lot of shares. @Cai how many shares do you have? I mean shared folders. The number of other clients in my situation is not that large but I have roughly 30-40 folders i'm sharing. Note that the above memory footprint was after fully shutting down Resilio and waiting for it's memory to be returned to the OS before starting and as this graph shows I've done zero on the network since then: