Ah! That works exactly as I suspected it would. Therefore, I was running the old version.

How, you ask? (Need I remind about the "stupid I have yet to use?") The old make install put the binary in /usr/local/bin, rather than /usr/bin. My Pi4 $PATH order has /usrlocal/bin prior to /usr/bin, so it finds the old compile first rather than the new version, that now lives in /usr/bin (which is probably less confusing for most folks).

jon@pi4~$ which indi_wmh_focuser
/usr/local/bin/indi_wmh_focuser # doh!!

I am happily running the new version and found the Abort button (right where you put it). You may rest easy now, confident in the knowledge that if...er..when.. I fat-finger a relative position as 30000 instead of 300, I now have an option to resolve the issue rather than going into town for dinner and coming back when it may be finished.

Your assist is much appreciated!