Are Muslims allowed to work in a bank, even if it's labeled as sharia bank?
As discussed in this previous answer, working at usurious banks (banks that profit through interest) is forbidden.
As for Sharia-compliant banks, working for them is permitted if they are truly Sharia-compliant. Some banks are only Sharia-compliant in name, or they offer Sharia-compliant services alongside usurious services. So before working at such a place a person should do their own research and find out if the bank is truly Sharia-compliant. Even if the bank claims to have a fatwa from a scholar that rules their services to be Sharia-compliant, a person should look at the bank critically. If you are unable to decide whether a particular bank is really Sharia-compliant or not, ask a knowledgeable person to do some research on the bank.