It is compatible.. it's simply the latest versions that require a more recent version of PHP. You can always download the older versions via the History
tab. You will need to check the update log also to see when the higher PHP requirement was put into place.
That's one of the hazards of not upgrading... you do reach a point where you are limited on the add-ons as they continue to progress onwards and raise their requirements.
I do agree that since it is requiring PHP 8.x the 2.1 compatibility tag should be removed though and it denoted that the older versions do run on EOL PHP versions.