A minecraft fabric clientside mod to restore sword blocking, you just need a shield in your offhand.
Works especially well if you want to use 1.16 on a 1.8 server that is running ViaVersion.
I recommend using this together with Item Model Fix, because it looks a lot better without these seams.
Should be allowed on every server, since it doesn't give you an unfair advantage, as it only changes the visual part of blocking.
If you are looking for a mod that allows sword blocking without a shield, take a look at Parry.