How to diagnose a slowdown?

I’m sitting at 80% memory usage. Is this typical? The dip is because I stopped and restarted the app using the launcher.

droplet: 4 GB Memory / 2 AMD vCPUs / 80 GB Disk

I spun up a new droplet and put in a backup of the forum (without images) and I get similar behaviour

htop output, sorted by mem: