Can one daven mincha after shkiya?
Yes, up to 20 minutes after sunset
only bdieved, right? its still ideal to daven before shkia
One should make a condition when davening 10+ minutes after shkiya. If it’s still day, this counts for mincha and the next Tefilla is Maariv. If it’s already night, this is Maariv and the next Tefilla is Tashlumin
do the same rules apply for mincha on friday?
One should definitely try to davem before shkia. If not there’s a few minutes leeway and previously mentioned. However it wouldn’t help to make the aforementioned condition