Watch the video:
Timestamps:
0:00 - Normal behaviour [No compatability]
1:01 - Plugin explanation
1:58 - ViaVersion [New version, Old server]
3:29 - ViaBackwards [Old version, New server]
5:00 - Backwards and Forwards compatibility on a server
5:21 - How do new, missing items work?
Want to host a server and allow clients to join, regardless of their version? Don’t want to update the server, or force clients to update? Well, with simple plugins, you can make your server backwards and forwards compatible! Allow outdated and updated clients to join your server! This video shows 1.14 and 1.16.2 clients joining a 1.16.1 server, for example, but this works for a bunch of different version combinations.
ViaVersion [Forwards]: https://www.spigotmc.org/resources/viaversion.19254/
ViaBackwards [Backwards]: https://www.spigotmc.org/resources/viabackwards.27448/