I have the Show incompatible versions checkbox in the stock f-droid client set to off (which is the default), and I have the Guardian Project repo turned on (I don’t remember but I think this is also the default). When I open the Guardian category, I see a Checkey app with an Incompatible warning next to it.
Rather, I have not expected to see that app listed at all, because (to my naive understanding) it seems to meet the “incompatible” condition, and (to my understanding) the settings says not to show such apps.