Absolutely, but you'll need to use the room code system.
The FitXR room code system for sending multiplayer invites is cross-platform, meaning Quest and Pico users can join the same multiplayer lobby. If you need help getting a multiplayer lobby started then you can read this guide.
The "Invite Friends" button that Quest users will see is a Meta exclusive feature, and so can't be used to invite Pico users into your lobby.
I've been sent a code but I'm not sure what to do with it?
No problem at all, we've written a guide here that explains how to use your room code.