I use Thunderbird as my main Matrix client since it's already always open on my PC and is Lightweight. Whenever I open Element or any other client (Nheko, etc.) they all complain about each-other being unverified.
Clicking verify in any client does nothing. No popups in any other clients - doesn't ever seem to do anything. Sometimes Element will pop up a QR reader but there's no QR presented in the other clients. The UX around Matrix is a nightmare.
Not sure how often they update these pages, but Thunderbird is still listed as beta on matrix.org clients page [0], and I remember trying it out some time back and it was indeed very beta (maybe not even beta). It didn't feel like it was getting much maintenance so I stopped using it. I think it's fair to expect bugs in beta releases.
Clicking verify in any client does nothing. No popups in any other clients - doesn't ever seem to do anything. Sometimes Element will pop up a QR reader but there's no QR presented in the other clients. The UX around Matrix is a nightmare.