hi, i've a few problem rfom installing a HAP AC2.
I"ve connected with eth1 the router to my internet box. My box have dhcp server with 192.168.1.1/254 adresses.
I've put the HAP in a dual home AP with internet adress in automatic (192.168.1.165 with gateway = 192.168.1.1)
My local network is 192.168.88.1 with DHCP server and NAT.
All work fine, i can connect to the router and internet but all connected cliets have adresses with 192.168.88.x.
How it is possible to have local adresses with 192.168.1.x managed by my internet box ?
i've tried to put in local network ip adress = 192.168.1.1 (gateway) and hdcp server + nat selected but it doesn't work.
Can you help me ? And sorry for my english.

Then why do you use 192.168.88.XXX LAN addresses? If that's your LAN and you Use NAT then it's normal clients to (must) have 88.XXX addresses. Why using NAT on the MT device?
As I see it, it should just be an AP, disabled DHCP and NAT, and let your internet box manage everything in the 1.XXX network.

i want to access to devices connected to my hap ac2 from an other router also connected to my internet box and with this configuration i can acces to a 192.168.88.x address.
If if remove NAT i have no more internet access.
if i remove dhcp server what adress i've to put as local network ? I've tried with 192.168.1.1 (gateway of my box) and 192.168.1.244 for exemple it doesn't work

The issue is not NAT or no NAT, but the route (and potentially firewall).

Firewall:
WAN i/f traffic is blocked to access hap ac2 etc. (default means all outside ETH1 port is considered "outside").

Route:
neither clients on hap ac2 nor your other router clients know how/where to reach each other!
Add a route on each router, and you can keep subnets and NAT (if you want):

/IP route
add route 192.168.my-other-router.subnet/24 gateway 192.168.1.my-other-router-IP
Now hap ac2 knows that example 192.168.120.4 (if this would be a client on your other router subnet) routes to your GW and from there to the other router.

And add corresponding route as well on the other router.
Now you can ping connect from each other if firewall allows connection.

Well I think a diagram will help immensely sort out what is being attempted here.