@Technomann-2 Thanks "Clive" but that response is NOT very helpful. If you don't have any insight into this issue then please do NOT respond at all. That's a very DUMB thing to do...

  @Technomann-2 

It is not so easy to estimate what your problem is from the description of the problem. it doesn't work on wired router but on wireless router it works you say, do you have two routers?? try to explain the problem a little better. no one on the forum can guess what you mean.
As for the wireless router why are you using it? if you don't know what you're doing, it can cause problems, I've seen that many times, a typical mistake there is that the wireless router is connected to the LAN with the WAN port. then you get two different networks with a firewall between the LAN and the wireless router.

try to explain how you have connected your network components.

  @MR.S There is NO wireless router. I only made that comment because the title of the forum was "Wireless Routers" and I could find no forum for wired routers...

I will attempt to explain the problem again in a more detailed fashion: I set up the TP-Link Multi-WAN Wired VPN Router Omada TL-R605 as my main router for my home network. The signal comes in from the ISP to the modem, and from the modem I have connected via cat 5 ethernet cable to the WAN port on the TL-R605. Basic stuff, right? All other devices are connected to the LAN ports on the TL-R605 -- my PC, the printer, and a small home server -- the ASUSTOR NAS -- that I mainly use for backups. Before I installed the TP-Link Multi-WAN Wired VPN Router Omada TL-R605 I could connect to the dashboard of the ASUSTOR NAS via any web browser, simply by typing the LAN IP address into the URL field of the browser. Now, however, this is no longer possible. Whenever I attempt to I get the error:

Unable to connect

An error occurred during a connection to 192.168.0.133.

    The site could be temporarily unavailable or too busy. Try again in a few moments.
    If you are unable to load any pages, check your computer’s network connection.
    If your computer or network is protected by a firewall or proxy, make sure that Waterfox is permitted to access the web.

Which I suspect is due to the firewall on the TL-R605. If it is a problem with network address translation, how do I resolve it?

Than you for your assistance and for not engaging in name-calling...

  @MR.S There is NO wireless router. I only made that comment because the title of the forum was "Wireless Routers" and I could find no forum for wired routers...

I will attempt to explain the problem again in a more detailed fashion: I set up the TP-Link Multi-WAN Wired VPN Router Omada TL-R605 as my main router for my home network. The signal comes in from the ISP to the modem, and from the modem I have connected via cat 5 ethernet cable to the WAN port on the TL-R605. Basic stuff, right? All other devices are connected to the LAN ports on the TL-R605 -- my PC, the printer, and a small home server -- the ASUSTOR NAS -- that I mainly use for backups. Before I installed the TP-Link Multi-WAN Wired VPN Router Omada TL-R605 I could connect to the dashboard of the ASUSTOR NAS via any web browser, simply by typing the LAN IP address into the URL field of the browser. Now, however, this is no longer possible. Whenever I attempt to I get the error:

Unable to connect

An error occurred during a connection to 192.168.0.133.

    The site could be temporarily unavailable or too busy. Try again in a few moments.
    If you are unable to load any pages, check your computer’s network connection.
    If your computer or network is protected by a firewall or proxy, make sure that Waterfox is permitted to access the web.

Which I suspect is due to the firewall on the TL-R605. If it is a problem with network address translation, how do I resolve it?

Than you for your assistance and for not engaging in name-calling...

  @Technomann-2 

so what you're trying to do is simply LAN to LAN communication, which router you use should have no influence on that, the router gives out an ip and then the router doesn't do anything with the communication as long as it's not LAN to VLAN.. but I'm still confused that you mentioned that it worked via the wireless router (which you don't have) did you mean WiFi or somthing, are you sure the device you're trying to reach has the same ip as before you changed the router, is it fixed ip or does it get ip from dhcp?

  @MR.S Before I purchased the TP-Link Multi-WAN Wired VPN Router Omada TL-R605 I had a Netgear wireless router connected to the modem. That allowed me to connect to the ASUS NAS interface simply by typing the proper LAN IP for the NAS via any web browser. I have now configured that router as a WAP -- Wireless Access Point -- but most of the time it is not even turned on, so that router does not even enter into the equation of the current problem.

The TP-Link Multi-WAN Wired VPN Router Omada TL-R605 assigns IP addresses to local area devices via DHCP, however one can "reserve" an IP for any specific device once it has been assigned automatically. The DHCP server assigned an IP of 192.168.0.133 to the ASUSTOR NAS, which I have now reserved or pinned to that device. The question remains, why can't I access the NAS control panel interface which I used to be able to do with the Netgear wireless router. For example, if I open any web browser on my PC and type in 192.168.0.1, the log in screen for the TP-Link R605 Gigabit Multi-WAN VPN Router appears, and I can log in and access all the configurations for the router. I should be able to access a similar dashboard for the NAS, but I can't...

  @Technomann-2 

before we go further, upgrade the firmware on the router, the first versions were extremely buggy

https://static.tp-link.com/upload/firmware/2023/202312/20231221/ER605(UN)_v1_1.3.1%20Build%2020231207.zip

  @Technomann-2 

Before I purchased the TP-Link Multi-WAN Wired VPN Router Omada TL-R605

If you've recently bought that, then for a start I'd request the supplier replace it with a v2 !. You have a v1 which is already end-of-life https://www.tp-link.com/uk/support/faq/3562/

and will receive no more firmware updates.