TPLINK Archer C60 v3 Troubleshooting

I have a new router with a fresh install of OpenWrt, and an old router that I wish to replace.
The problem is that I'm unable to connect to the internet when plugging to the WAN port of my new router the ISP's cable.
ISP -> NEW-router-WAN-port -> NEW-router-LAN-port -> PC

There is no connection with this setup after closely following the wiki guides and checking according to this thread if there was a problem with my ports assignments which appears to not be the case since:
when connecting the new router's WAN port to one of the LAN ports of the old one, while its being connected to the ISP's cable, DHCP on the new router works fine.
ISP -> OLD-router-WAN | OLD-router-LAN -> NEW-router-WAN | NEW-router-LAN -> PC

I've already passed my inquiry to the ISP and they told me to try and use an static IP to connect to their ONU, which I did. They insist there must be something wrong with my router.
Also uptime connection is shown and packets are moving to somewhere because the interface say so, but I have no internet connection.

What type of internet do you have? Cable? ADSL?

If you connect the cable from your ISP directly to your laptop, does the internet work? Do you get an IP? How does your ISP assign IP address?

I have Cable internet.
Whether I connect my computer to the ISP before or after the PoE injector from where the old router was connected, my internet does not work. I tried with a Windows laptop and my computer, which runs Mint. Not tweaked any configurations whatsoever, just plugged the cable and this is ifconfig output:

enp8s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet6 fe80::7725:b360:6d8a:404a  prefixlen 64  scopeid 0x20<link>
        ether 18:c0:4d:3c:ba:8f  txqueuelen 1000  (Ethernet)
        RX packets 117169  bytes 75000006 (75.0 MB)
        RX errors 0  dropped 75  overruns 0  frame 0
        TX packets 96506  bytes 10195730 (10.1 MB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet  netmask
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 6260  bytes 562862 (562.8 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 6260  bytes 562862 (562.8 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

wlxe894f60c4c00: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        ether e8:94:f6:0c:4c:00  txqueuelen 1000  (Ethernet)
        RX packets 6327  bytes 7332342 (7.3 MB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 4049  bytes 513636 (513.6 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

So I assume they are not assigning an IP.
Regarding your last question I don't know with certainty how does my ISP assigns IP addresses, but the technician to whom I spoken previously mentioned that the ONU assigns them automatically. I assume it stands for Optical Network Unit, and that's all I can confidently say about it.