@retiolus Just to be clear, you have the whole OS installed on that external SSD and you boot Rpi4 from that?
As long as you boot from an SD card, you should see all the files normally on the new Rpi 5. But there are probably going to be differences, because the Pis use different CPUs.
As long as you just need to access the files saved on the SSD, it should be okay.