While holding up a shield, swords won't work, nor will anything in the hotbar which has a MOUSE2 command.
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I remember at minecon they mentioned about having a lefthand view so you should be able to fight with sword in left hand and then block but holding a shield in main hand and sword off hand you cant actually attack
I'm currently having this exact problem in 1.20.1 does anyone know if I can fix it or will I have to wait till the next update?
also given I'm in a different version then listed should I write a separate bug report?
This behavior works as intended per MC-86141. It is not considered a bug and will not be fixed. Please don't create a new bug report about it.
swords don't block anymore and therefor don't have a mouse2 action any more.