AX5200 Lan setup not working

> [...] Router will NOT [...]

   "will NOT" is not a useful problem description.  It does not say what
you did.  It does not say what happened when you did it.  As usual,
showing actual actions (commands) with their actual results (error
messages, LED indicators, ...) can be more helpful than vague
descriptions or interpretations.

   What happens when you try?

> [...] put all devices to lan setup ip address. [...]

   ADVANCED > Setup > LAN Setup : Address Reservation?

> [...] Nothing works. [...]

   See "not a useful problem description [...]", above.

> [...] I have 70 devices 36 are smart devices ( Blubs, switches,
> camers......).

   That may be too many.  Besides any limit on address reservations, I
seem to recall seeing a limit of 32 devices per radio.  If all your
Internet-of-Junk ("smart") devices use 2.4GHz, then having 36 of them
might be another source of trouble.

   Adding a wireless access point could reduce the number of devices per
radio.  If the DHCP server in the router simply can't/won't handle that
many address reservations, then you'd need to use a separate device as a
DHCP server.  Raspberry Pi?

   Why do you need to reserve an address for every device?