I see wrong assumptions about how Wi-Fi works mixed with wrong expectations, followed by wrong hardware suggestions. Read below and you'll know what to do.
- in a 55 square meters apartment what "range" the AP offers practically doesn't matter
- if the old RT-AC66U can cover the place, any modern AC or better class AP will also do it
- your phone will see zero battery life improvements with AX TWT, not working as expected
- your phone has nothing to do with Gigabit connection, even with >100Mbps connection
- you perhaps don't have 10 users, but 10 devices and not all of them active at the same time
- you run pfSense appliance with native VLAN support, but no home router has native VLANs support
- Beamforming and MU-MIMO require distance and different directions, plus client support
- 4x4 AP doesn't automatically split streams to multiple devices, see why in the comment above
- OFDMA MU-MIMO in AX can serve multiple clients simultaneously with 2x2 radio, in case it works
- I would disable all Beamforming and MU-MIMO in your environment for perhaps better performance
- your country has different Wi-Fi regulations and user experience in US may not be relevant to you
- your country has different Wi-Fi channels available and equipment purchased elsewhere is not a good idea
- 160MHz wide channel is not guaranteed, it requires DFS channels, it also reduces the AP range
- for stability I do not recommend using 160MHz wide channels, especially in a condo environment
- AX to common 2-stream client @80MHz channel won't improve significantly your experience
Skip the
unpopular (at least here on SNB) and
buggy (Wi-Fi issues feedback everywhere) Asus RT-AX68U, skip expensive and perhaps unpopular in your country Zyxel products. Go to a local computer store and get what you know works well from your experience and in your country - UniFi, Omada, etc. You don't really need AX support - AC Wave 2 will be a huge improvement over Asus RT-AC66U
* and can do 550Mbps to common 2-stream AC client. AX class AP won't improve anything further. In your small place you'll get ISP line speed to every client, upload and download, plus headroom for ISP upgrade to ~600Mbps. This is what your APU2C4 board
** can do for IDS/IPS anyway, in case you run it and it's multi-threaded (Suricata). Get a business class AP with stand alone mode (not cloud/controller configuration only), with native VLAN support (you may want to run a Guest Network), with injector for PoE. You'll save money, time and frustration.
* - this is the first AC class Asus router with BCM4360 radio and BCM4706 MIPS single-core 600MHz CPU. The radio SoC doesn't have own processing unit and relies on the main CPU. You have noticed perhaps this router struggles with >250Mbps on Wi-Fi and CPU utilization spikes a lot when Wi-Fi is under load, even when stripped to AP only duties.
** - what
@Tech Junky doesn't know is APU2C4 is a single board computer made for router/firewall applications with non-replaceable NICs. AMD GX-412TC quad-core 1GHz CPU is there not for high performance, but for power efficiency. The board is excellent for your use with under 20W total power consumption, depending on configuration.