Using Windows 11 start menu on Win10 21H2 (19044.1620) over 2 monitors.
Start11 Options >> Start Button >> Related >> "Center aligned"
- sometimes both of the start buttons are centered (hooray!)
- sometimes the left monitor's start button is on the left while the right monitor's start button is centered
- sometimes it's the reverse: left monitor's button is centered while right monitor's on left