Sadly, SteamVR on Linux continues to have quite a lot of quirks and over time it's gotten a little rough, here's a way to fix the SteamVR Overlay not working.
One of the most annoying bugs right now is how the SteamVR Overlay doesn't seem to work. Not just that, but even the settings menu from the main SteamVR menu doesn't seem to work either. This appears to be a problem on any Arch-like Linux distribution (EndeavourOS, Manjaro etc) and seems to originate with the vrwebhelper.
Thankfully, some clever people on the official Valve GitHub found a way to get it all working again and it's pretty simple.
First, find where SteamVR is installed, somewhere like this:
Open the file "vrwebhelper.sh" and replace this line:
Now you need to download an older version of freetype2, which another helpful user put up on a download link (web archive in case it vanishes) and then extract the files from the archive into the "vrwebhelper/linux64/" folder. After that, it all works just as expected again. Nice!
Hopefully Valve will get around to solving this soon, perhaps once they've got a few hands free after the Steam Deck ships, which they're clearly putting a lot of their effort into right now.