I did the same thing a few months back, replaced the 3B with a 3B+ and swapped the microSD card into the new board to get a little more speed from the green monster. My 5GHz wifi is working fine however. I haven’t reflashed, but have ‘updated’ via the OS menu item which hasn’t stopped my 5GHz wifi working. According to my “About” screen, I’m running build 2023-05-23 number 25.
If you run a
cat /proc/cpuinfo | grep "Model" does it report a Raspberry Pi 3 Model B Plus Rev 1.4? Have you tried the 3B+ with standard raspian or kali connected to a keyboard, mouse, video and power, without using the Pi-Top3 to ensure you have the right board?