On your OpenWRT device go to the MiniDLNA menu and at the top of the page you should see something like "miniDLNA is active and serving ...files.....". If this message is not available then you need to check your config first. There is not much to config other than specify the media directory which must be preceded by an A, V, P
If your config on the AP is good (i.e. miniDLNA says it is active and serving x number of files) then test that the service is available over your LAN by pressing Windows Key + R and type in CMD and enter to get the command prompt then enter:
telnet 8200
If DLNA is working you will see a blank screen and you can hit enter multiple times to force close the session. If telnet gives an error connecting you have a firewall issue either on your AP or your Windows firewall on your desktop.
HTTP/1.1 501 Not Implemented
Content-Type: text/html
Connection: close
Content-Length: 149
Server: DLNADOC/1.50 UPnP/1.0 MiniDLNA/1.3.0
Date: Sun, 27 Mar 2022 13:08:26 GMT
EXT:
<HTML><HEAD><TITLE>501 Not Implemented</TITLE></HEAD><BODY><H1>Not Implemented</H1>The HTTP Method is not implemented by this server.</BODY></HTML>
your TV must support DLNA. If you are sure it supports DLNA then it should automatically discover the miniDLNA server.
For your PC download and install VLC player then open VLC player and click on browse network. VLC should automatically discover the miniDLNA service and you can click on your mp4 or mp3 files to play them in VLC. If VLC is able to discover the service then your TV is not DLNA capable.
yeah ok now that makes sense why your TV and PC can't see the miniDLNA service on the router. I don't know the exact specifications of DLNA but I think it limits its service discovery to the same IP address space and subnet. I don't think DLNA is even routable so you can't try to route it to another address space.
The immediate solution is to move your PC and TV into the 192.168.11.0/24 address space. If 192.168.31.1 is simply acting as a repeater then try to configure the repeater into the 192.168.11.0/24 address space which will solve your issue.