What do you mean that you tried multiple ways?

For the heck of it, I would run updates on the program for both years.  Then I would reboot my computer.  Next I would open the client in the 2023 program and see if the client data looks intact.  If it does, I would try the transfer function again.  If the client still didn't transfer, I would try making a copy of it in 2023 and see if the new file would transfer.  If that doesn't work I would give up and start the client from scratch in the new year.  But if it is a client that has a huge amount of data, I would consider calling support.  And then after a couple minutes my mind would be clear of silly ideas and I would just start inputting the client from scratch.