I know (1) dragging the tab bar downward will result in creating new
windows for the tab (2) But this happens even if you just click it.
(1) Yes - default behavior.
(2) No - not here, several machines, should not happen
Things to try:
(A) Repair Edge: Settings, Apps, Installed Apps (Apps and Features), scroll down to Microsoft Edge, 3 dots (...), Modify and the Repair. Restart computer.
(B) DISM and SFC:
(1) Open cmd.exe with Run as Administrator.
(2) DISM.exe /Online /Cleanup-image /StartComponentCleanup
(3) DISM.exe /Online /Cleanup-Image /Restorehealth
(4) SFC /SCANNOW
(5) Restart when all the above is complete and test.
This should help get Edge working correctly.