For heavens sake, its a six and a half gig download !
mgc, I cannot replicate your problem. I guess you are using the Gnome Desktop ? Thats what I just tested. You can install my app, tomboy-ng, its in the official Ubuntu repo, just "sudo apt install tomboy-ng". tomboy-ng is built from FPC/Lazarus. See how that feels.
Just to be sure, I pulled another, recently built binary from my Debian Bookworm, it works fine too.
Honestly, Ubuntu is slow, the Gnome DE is dreadfully slow, that might be all you are seeing. If you must use Ubuntu, I'd suggest choosing Mate or XFCE, even Cinnamon.
Next step might be to specify exactly what you mean by 'slow' ? eg "it takes 8 seconds to load", "it takes 14 seconds to compile Lazarus" - something we can compare to ?
Tomorrow, I might have time to install FPC/Lazarus on the VM, so, if you have some numbers ...
Davo