@Stuart ********
24 miles was the limit that i recall, but with a visa this doesn't apply. I'm not sure whether any of the Burmese land borders are now allowing entry with a visa again, which was the case pre Covid.
All I know is that Mae Sai-Tachilek allows travel to Kengtung on a border pass (obtainable on arrival) and requires a guide (both for Thais and 3rd country foreigners like most of us).
The other border crossings currently allow only a bounce or maybe, limited travel from the border.
Since they're asking for Covid documentation (whereas Myawaddy is not) I assume that spending the night on the Burmese side is now permitted at Kawthoung but you can't travel too far from the city. I can't imagine them asking for Covid documentation on the Burmese side just for a bounce, which is why Myawaddy isn't, because you can't enter the city there, only do a bounce (even though if you were permitted it would be day return only, same as what Thais are allowed).