Macbook issues with Deco X50 router

Next, if you can get in range of the troublesome access point, but not connected to it, you can still examine its raw signal strength (RSSI) in:

 menu >about this Mac> (System Report) > Network (second group) > Wi-Fi

signal strength needs to be above (closer to zero than) -70 to make any meaningful connection.

You can only get a local "good" IP address when you can log in to from that computer to that exact router. Perhaps the network password is stored wrong.

Try deleting that as a preferred, log-in-automatically selection, and it should invite you to log in again, and re-specify the password.

Generally, best results are obtained by using the same network-name for all Access points.

Every device gives it self a "self-assigned" IP address to identify itself on the local network. Typically, it is replaced so quickly, you would swear "self-assigned" IP addresses did not apply to you.

When you keep your self-assigned address instead of transitioning to a local IP address, that indicates a connection problem, specifically, you can not connect back to the Router to get a good local IP address.

If limited to exactly ONE MacBook Pro, make sure you have RSSI of better than (closer to zero than) -50 when very close to a Router, as a check against disconnected antenna wires inside.

Hold the Option key while you click on the Wi-Fi icon son the MenuBar for a snapshot, like this older one:

.

<< I'm standing 1-2 meters far from Deco>>

Then do you have RSSI of -50 or better?

The 'better than -50' check will tell you whether the antenna wires are disconnected internally.

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There are LOTS of posts about Mac Wi-Fi, but each "network neighborhood" is different, and the signals are radio signals, so users have many and varied individual issues.

There are no pervasive issues with MacOS Wi-Fi. Having another MacBook Pro on hand will not provide additional insights.

However, there are LOTS of software packages you could install that would poison your network performance.