In the crossplay era, when big games seek a single account on all platforms, Rockstar Games is doing a completely different trick: your character in GTA Online will not be available on old consoles if you want to move with it to a new generation.
Nuance identified on the official Rockstar support site:
So moving the profile to a new generation is called "cut out, insert," not "copy, insert." In Reddit's commentary, it's already called the "deepest decision."
Eyewitnesses say that in the past, when Rockstar allowed the GTA Online character to be moved from PlayStation 3 or Xbox 360 to PlayStation 4 or Xbox One, the original profile remained available. Therefore, a new character could not be created from scratch on the previous console (although progress between generations has not been synchronized).
There are a lot of underwater rocks in the GTA Online in principle: let's say you can move from PS4 to the Xbox Series, but then you'll lose the GTA-- they only exist within a single Consol family, and if you've moved the profile from PS4 or Xbox One to the PC, you can't put it on the PS5 or Xbox Series now (the truth is, Rockstar already promised to fix it).
It may not be possible to make a full-fledged crossplay with a minimum of trouble in GTA Online, as the last generation of devices (including PCs) are going to introduce exclusive content.