Ever solve your problem, ryck?
Not yet. Where it had occurred at a particular site, I recently had it happen at another although, at the new site, it was different.
At the first site, the Captcha simply did not work. At the recent site the Captcha worked once but, when I tried to go in a second time, it did not. However, at the second site when I shutdown Safari (V 14.0) and rebooted it, the second site Captcha did work. Note: The second site was a government site for voter registration and perhaps the site was being cautious. The first attempt was my registration, the second my wife's.
Jon provided an Apple number to try but, with my slowness issue (computer, not me) and pressing matters related to my Pensioners coalition, the Captcha problem had to get to the back of the line, so I have not yet called.