The message
from "mentalguy2004" contains these words:

How deep would I have to
concrete to support the weight of the bike?

A couple of inches would be plenty, though three might be easier to lay.

If you want a good solid anchor then dig a pit into which you can set a
hardened chain, Aldi have some at the moment. Sink it a foot down and
tamp the concrete well round it.

--
Skipweasel
Pay no attention to that man behind the curtain.