Sorry, but the video is so fast that I cannot understand what is happening in it. I am trying to understand what you mean by compatible. I can use other instances to display my Fediverse profile @danielhz@mastodon.social. For example, in the Mastodon instance https://mamot.fr/ and in the Kbin instance https://kbin.social, my profile is then displayed on the following URLs.
A: https://mamot.fr/@danielhz@mastodon.social.
B: https://kbin.social/u/@danielhz@mastodon.social
These URLs are displaying what can be seen on the original URL:
C: https://mastodon.social/@danielhz.
Moreover, I can do the same with a post. The URLs D and E (below) are displaying what can be seen on URL F.
D: https://mamot.fr/@danielhz@mastodon.social/110680082727181778
E: https://kbin.social/m/fediverse/p/748374/I-created-a-profile-on-Kbin-at-danielhz-at-kbin-social-and-a-profile
F: https://mastodon.social/@danielhz/110680082409708996
If I use wget to access URLs A, B, C and D, I got the following results:
For A, I got a redirection to C, and then download C.
For B, I download C.
For D, I got a redirection to F, and then download F.
For E, I download F.
Then Mastodon and Kabin have a different behavior when trying to access “copies” of a post. Is this the difference you mean by compatibility?