STAND no longer works properly since latest IOS update (18)

In that case, if you were to call Apple support they would say:

1) Force restart your watch and phone

if that doesn't fix the issue

2) un pair your watch then pair it back setting it up as new.

That is basically your only trouble shooting steps you can do if it worked in the past.

Stand does not mean "stand" it means "Stand and move around"

Standing in the kitchen at a counter preparing food will not count even if you're there for 2 hours.

If you walk around for over 1 minute taking steps or swinging your arm it will count.

In fact you can get credit for stand hours while sitting on the couch if you swing your arm up and down and wave it for over 1 constant minute.