Well you learned a hard lesson. Wireless is not all it seems and unless you have a very expensive pro system then wireless gets saturated in a system like yours.
Luckily I put conduit round the place, so I could hard wire the two AV systems. When we were on 50 MB up and down, which was the highest we could get, until a couple of years, ago, the system would easily saturate when guest were here,
As soon as we could get 250 MB up and down I jumped on it. All cable was replaced with cat 6 and all AV equipment is hard wired. Now we can have the place full of guests and not a problem
Lastly wireless does not like 5G or the devices don't. 2.4 G is much more stable, which is probably why Musicast does not support 5G. 5G has much poorer range, does no like going though walls and has many more drop outs. So I have all iPhones, iPads and laptops connected to 2.4. I make sure of that with guests now.
With much higher stress on networks, many much more experienced than I are recommending to hot wire as much gear as you can and leave the rest that must be mobile to wireless. If you think that I believe wireless is oversold you are correct. It has not kept up with current network demand at an affordable price. It can be done, but you need to drop a lot of change to develop a high bandwidth reliable wireless system. Google professional routers.
Lastly many if not all consumer routers have dodgy software. I had to get rid of the software on my top of the line Linksys router and install open source public domain software. I could rant and rant about consumer wireless gear, but I think that is enough.