hello, I got same problem here. Screen capture freezes frequently, not always, but still happened
especially when I try to share screen capture
device iphone 12mini, ios 14.3
its doesn't happen on my old device iphone 6s
here is one recorded when it happened, battery , storage, network connection no problem.
https://youtu.be/9Nn0S6JZOjI
you can see capture function does work immediately until 50sec after.
I still could swipe until capture function pop up, than freeze for few second.
I tried to looking for help at local repair center.
They got no idea with this issue, and help to reset device, but problem doesn't solved.
And there are few cases similar on our community.