Never go for ranger extenders or power line adapters unless no choice and last mile or to cover wifi dead zones for low bandwidth devices.

Deco X20 is ax1800 rated. If you intend to cover the whole house perimeter , then go for mesh, or get another TP-link router which has easy mesh function, eg; ax53 or ax55

For your current speed, best get AX3000 rated and above to ensure your routers+mesh can dish out 800Mbps.
If your concern is only extending WiFi coverage and range only, my suggestion just go grab a 2nd hand router and set is as wireless repeater.

If you want speed and coverage, your only choice is using wired backhaul, the good thing, can be mixed and match with any desired router or mesh. Bad thing, you need to headache  for a while on how to set up the cat5e cables.

With the rise of much faster Internet speed, this post serves as a generic guide to know what Wireless Router you should buy and some generic tips and tricks when buying a router.

Use the format below if you wish to ask what router to buy
Recommended Router List
RM200-400: TP-Link AX55
RM400-600: TP-Link AX72/AX73, ASUS TUF-AX4200, ASUS RT-AX57
RM600-1000: TP-Link Archer AX80, ASUS TUF-AX6000
RM1000 and above: Most routers beyound this price point are good

Equipment List
This list serve as a reference on what router you should purchase based on the performance of their WiFi tested with Intel AX200 Wireless Adapter. Unless specifically mentioned, these routers can support Gigabit speed over wired LAN.

WiFi router speed rating

All the routers tested below support Unifi unless stated otherwise.
Only ASUS router support Maxis with VOIP working properly.

Note: For routers that appeared twice in the list, it means that the performance level is somewhat middle.

TP-Link
100Mbps: Archer AX12
300Mbps: Archer AX23, Archer AX53, Deco X20, Deco X50
500Mbps: Archer AX55, Archer AX72/AX73, Deco X50, Deco X68
800Mbps: Archer AX72/AX73, Archer AX80, Archer AX95, Deco XE75, Deco X80, Deco X95
>1Gbps: Deco X95, Deco BE85

Asus
100Mbps: RT-AX1800HP
300Mbps: RT-AX1800HP, ZenWiFi XD5, RT-AX57
500Mbps: ZenWiFi XD5, RT-AX57, TUF-AX4200, ZenWiFi XP4
800Mbps: TUF-AX4200, TUF-AX6000, RT-AX86U PRO, GT-AX6000, GT-AX11000, ZenWiFi XT8, ROG Rapture GT6
>1Gbps: GT-AX6000, ZenWiFi XT12/ET12, GT-AXE16000
What WiFi adapter to buy?
Here are the only WiFi adapter that I filtered that are decent.

PCIE Wi-Fi 6 Adapters:
Performance are the same since they all use the same solution from Intel.

TP-Link TX3000E	3 years warranty with external antenna cradle.
TP-Link TX50E	3 years warranty without antenna cradle.
ASUS PCE-AX58BT	3 years warranty with external antenna cradle.
Intel AX200	You can purchase the Intel AX200 from Lazada and install yourself for notebook users.

USB Wi-Fi 6 Adapters:
Not recommended due to USB stability issues

It's time to upgrade. Deco M9 Plus is 2 gen behind.

IMO, I think Deco XE75 is at a very good price / performance ratio now.

What do you anticipate you will gain with a static IP address? additionally most of the ISP provide a dynamic private address for ip4.