Bridging Netgear AX8 AX6000 to AC 1900 C7000 router

> [...] I want to bridge my old Netgear AC1900 Model C7000 modem router
> wirelessly. [...]

   To do what, exactly?  Sadly, "bridge" is a term which is so broadly
used as to have become almost meaningless.  What is the actual problem
which you are trying to solve by using the C7000 with your main
(modem+)router (the CAX80)?

> [...] I will then connect my C7000 router to be bridged. [...]

   "connect" how?  Do you mean a wireless connection, or a wired
Ethernet connection, or what?

> [...] As you know the C7000 does not have a bullit to choose for
> bridging, repeater etc. You have to change router mode to NO and restart
> to obtain bridging mode. [...]

   If you mean ADVANCED > Administration > Router Mode, then that would
be exactly what you do _not_ want to do.  That would configure the C7000
as a modem-only (one meaning for "bridge"), and you have no use for a
second cable modem.

   If what you want is to configure the C7000 as a wireless access point
(another, sloppier meaning for "bridge"), and connect it to your main
(modem+)router (the CAX80) using an Ethernet cable, then that should be
possible.  See, for example:

      https://community.netgear.com/t5/x/x/m-p/1463500

That's written for a Netgear C6300-as-WAP, but the steps are about the
same for any other router (any make/model) which lacks a one-step WAP
option.  (I'd expect a C7000 to be very similar.)