Tray icon brings up menu rather than does specified action with xpad
Cannot tell for certain if this is a bug with this app or with xpad, but it works fine with Pop!_OS on xpad version 5.4, but not on Arch on xpad version 5.4. Clicking on the icon will bring up a menu rather than doing the action specified by the xpad preferences.
Something similar also happens to me both with XPAD and with the mega.nz icon. On what I understand it depends on an overlap of icons.This thing started doing it from the most recent versions (it seems to me from 43 onwards). To solve the problem install , the 42 version which (at least to me on Debian Bullseye 11) seems to work well!
By a menu you mean something like this:

If that's the case, it's because it's using libappindicator (or libayatana-appindicator) to show the indicator, which is actually the preferred behavior of this app, and in such case icon click can't be configured, because it's just not supported by the API.