It wasn't incoherent at all.
He was saying you have a second amendment right but like all rights, it is not unrestricted.
Just like the First Amendment. The government cannot breach your free speech right. That right is said to be unabridged. You still can't yell fire in a crowded theatre without breaking the law. That's because you have duties and obligations as well as rights.
It's a shame the US Constitution is so poorly drawn up, so that people spend all their time talking about me, when a society is a we. Rights claims aren't very interesting unless their limits are defined with respect to other people. If your freedom impinges on mine, then our so-called rights are in conflict. Unless you recognise that things like duties and obligations are part of the conversation, then all you get is stoopid assertions.
When people are angry, their grammar sometimes dissolves. But Biden was clearly saying he supports people's right to bear arms, within reasonable limits.
For myself, I prefer a society with no guns, except for those permitted to do so for some purpose or another. Gun ownership works better as a privilege, not a right.
Trump doesn't know anything in the first place. So that's a drawback of having a moron as a candidate.