I used to go to a Protestant Three-Self (legal) church when I lived in Wuhan. You hear and read all sorts of horrible tales but I never saw any direct persecution.
Where churches got into conflict was with things like building permits. To get those you have to pay a bribe to get to the front of the line. This is true of everyone not just churches because bribes are just ubiquitous when dealing with the party. The church wouldn’t pay the “tea money” so they could never get the paper work filed. The way they worked around that was to find out who the clerks were and where they lived and then evangelize them.
Catholic experience may be different
Resident Chinese were not supposed to attend a Christian Church, but they were always accompanied by students who, if asked, would just tell the authorities that they were there to study English and make sure their teachers got to and from church safely, not religion.
The authorities would just smile and wave them through. Don't know if this was because of the Beijing Olympics or just China showing a more gentle face when foreigners were around. I expect it was some of both. She was only 19 when she went and had a generally good experience but, of course, some interesting stories to tell as well. She did pick up quite a bit of Mandarin and said it wasn't that hard to learn.
“The way they worked around that was to find out who the clerks were and where they lived and then evangelize them.”
That is sheer genius; spiritual solution to a pragmatic, earthly problem.