@DanielGB 

If you really need to know, then you could try your luck with a free utility called "Nmap". It can give you an "Uptime guess", which, despite the name, actually works well more often then not.

Right now I can't test if works with the AX50, but here is the output when I probe another TP-Link router I have at hand:

nmap -v -O 192.168.1.1

Starting Nmap 7.80 ( https://nmap.org ) at 2020-09-07 18:13 ?÷?·??á?ê±
Initiating ARP Ping Scan at 18:13
Scanning 192.168.1.1 [1 port]
Completed ARP Ping Scan at 18:13, 0.28s elapsed (1 total hosts)
Initiating Parallel DNS resolution of 1 host. at 18:13
Completed Parallel DNS resolution of 1 host. at 18:13, 11.06s elapsed
Initiating SYN Stealth Scan at 18:13
Scanning 192.168.1.1 [1000 ports]
Discovered open port 139/tcp on 192.168.1.1
Discovered open port 80/tcp on 192.168.1.1
Discovered open port 445/tcp on 192.168.1.1
Discovered open port 1900/tcp on 192.168.1.1
Discovered open port 20005/tcp on 192.168.1.1
Completed SYN Stealth Scan at 18:13, 0.39s elapsed (1000 total ports)
Initiating OS detection (try #1) against 192.168.1.1
Nmap scan report for 192.168.1.1
Host is up (0.025s latency).
Not shown: 995 closed ports
PORT      STATE SERVICE
80/tcp    open  http
139/tcp   open  netbios-ssn
445/tcp   open  microsoft-ds
1900/tcp  open  upnp
20005/tcp open  btx
MAC Address: 30:FC:68:4C:__:__ (Tp-link Technologies)
Device type: general purpose
Running: Linux 2.6.X|3.X
OS CPE: cpe:/o:linux:linux_kernel:2.6 cpe:/o:linux:linux_kernel:3
OS details: Linux 2.6.32 - 3.10
Uptime guess: 0.039 days (since Mon Sep 07 17:17:30 2020)
Network Distance: 1 hop
TCP Sequence Prediction: Difficulty=254 (Good luck!)
IP ID Sequence Generation: All zeros

Read data files from: C:\tools\nmap-7.80
OS detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 14.15 seconds
           Raw packets sent: 1023 (45.806KB) | Rcvd: 1035 (43.821KB)