Custom Block Help

Hey guys.
I'm trying to make a custom block with a model I have on BlockBench.
The thing is, I need it to not replace any blocks from the original Minecraft game. And I need it to be a breakable block. I know it can be done with nbt but I don't know how.
I've looked at thousands of tutorials, but none of them work for me on my version of Minecraft 1.21.1.
Could anyone help me?