So I've had my Samsung QN65Q9FNAF for a couple of years now and I have it connected directly to the AT&T Fixed Wireless Internet modem via LAN cable. I've never had one bit of problem with Netflix, YouTube, Disney+, Tubi and other apps. Last week when I would turn the TV on, I would get an error message that there was no internet connectivity and I would click the OK button and it would go off. I would check it by using the YouTube or Netflix app and they both worked fine. I also checked the network settings and it showed that I was connected to the internet. This would happen everytime I turned the TV on so I just blew it off. Last night I started the Disney+ app and I kept getting the spinning circle and it would never load. I thought maybe there was a problem with the app so I removed it and searched for it to install it but when I would type in the "D" letter I would get an error message stating "The Samsung Server was down, try back later". This would happen for a while and everytime I would check the network settings, it showed that I was connected to the internet. I finally called Samsung Support and got a representative who asked me to hold down the home button for 12 seconds so he could remote in. I kept getting an error message that there was no network connection. He asked me if there was a way the I could disconnect from my wifi and connect through a hotspot from my phone or other device. I turned on the hotspot on my iPad and he remoted in and said there was nothing wrong with my TV and that my home internet is on 5GHZ and the apps would not work unless the TV was connected at 2.4GHZ. He told me to call my internet provider and have my internet switched over to 2.4GHZ and he hung up. I remembered that I have two SSIDs, one at 5GHZ and the other at 2.4GHZ. So I connected the TV to the 2.4GHZ and all the apps worked just fine. So why is it that for two years all the apps on the TV worked fine then all of a sudden some of them quit working until I connected to 2.4GHZ?
Everything gets updated over time and there can be issues with all updates. What is the current software version on the television? Have you tried a Smart Hub or Factory reset? Are there a lot of devices connected to the 5GHz Wi-Fi band?