Us
DOn,t care about dual case, as long as you are our citizen, we treat you as such ONLY. So tax issue better hire expert.
Giving up is not easy, tax issue must be completely resolved.
China
Giving up is not easy at all. Lots of things need to be resolved, hukou, tax etc. technically we all overseas are mostly still Chinese citizens. So visit china carefully if you happen to be anti ccp. Or visiting countries close to china. HK same case, giving up is difficult.
Applying is tricky also. There is this Chinese American girl representing china in Winter Olympics, seemed she was born in us ,American father. Did she formally give up us citizenship? She many time still in US, studying there. So she got GC? Unlikely. It is tricky, esp when politics is so tense now. This girl could easily say I love both nations, but reality seems not allowing that.