Sorry for the late answer, don't go to aternos support that much. They are able to join with the DYN IP. He migrated when he had to, when mojang accounts where no longer supported. He is on pc as am I. The Software is, as said, different. 1.19 and some modded. And with modded, i mean i made my own pack by downloading a shiz ton of mods, getting the cores and getting through all the errors, so i was left with a handy little pack that we were going to play. Which we ended up doing.
As of the screenshot, i am currently unable to send anything, as i'm away from my computer, but since he can join, i don't think i'll need it. Although i will say thank you for trying to help :).