I may not have had the same problem as you Munchoba, but I have had a similar. So I will give you an example that might show that there are several ways to solve the problem.
My network in the house starts by connecting to a service distributor, box on the wall that I also think of as a modem. From outside the house, there is a fiber cable attached to this modem and into the house goes a short ethernet cable (in my case a cat 6a) which connects to the router Technicolor TG799 vac Xtream which was provided by my internet service provider (ISP).
At the start I was using my router as a one-box-for-all solution. It contained a switch and a Wi-Fi-functionality as well. The Wi-Fi was supposed to serve a couple of Chromecasts, a so called smart-TV and a number of handheld devices and computers. The router had a wireless phone connected to it and it was also the starting point for a long ethernet cable going to my music room some 20 meters away on another floor.
About a year ago I started getting into trouble. The Wi-Fi was not quite up to it, it did not reach every corner of the house, and my dedicated music computer in the music room started having difficulties finding the NAS that was connected directly to the router. I tried a number of different solutions but not until the beginning of this year I managed to set up a network system that works without flaws.
I will try to outline how it works with special regards to the music played in the house.
I kept my ISP router (Technicolor TG799 vac Xtream) and did some alterations via its user interface. I kept the wireless phone attached to it but moved everything else at least one step away by adding a short ethernet patch cable running to a simple, unmanaged switch. From this first switch I ran one ethernet cable to a printer, one to the office computer (where I also do maintenance tasks for the system), one to a separate Wi-Fi access point (AP) situated central in the house above the stairs, and then the long ethernet cable to the music room. It ends in a connection to another (fancy but unmanaged) switch which also is connected to my Synology NAS where I keep my music library, and to my dCS Network Bridge (NB) which then is connected to my DAC and preamplifier etc.
The Wi-Fi in the router is totally disconnected (via software/user interface) and the Wi-Fi AP (Ubiquiti UniFi) placed in the roof above the stairs covers all the house and some of the garden. From my music room I can send signals from smartphone or touchscreen via Wi-Fi to the Minimserver on my NAS. The Mosaic app is in my handheld (phone or screen) and communicates with the Mosaic elements in the NB. It works very well and I am pleased with the sound. Furthermore I use my handheld devices to read pdf files stored in respective album folder on my NAS. I can of course reach internet this way if I want more information about a certain artist or piece of music. So far I never felt I needed Roon so I have not tried that.
Best of luck with finding your own best solution!