FIXED
Bought Xbox One controller two days ago intending on using with PC via Bluetooth. I experienced literally every problem described in this thread (disconnects, stutter to 5fps in AC: Odyssey, lag in recognizing button inputs, you name it). Tried enabling Xbox controller config in Steam - no improvement. Turned out the problem for me was that since I use Ethernet LAN (i.e. not wifi) I didn't have my wifi antenna hooked up to my Gigabyte z390 Aorus Master motherboard. Well, it's this same antenna that also picks up the Bluetooth signal.
Hooked up the antenna tonight and instantly all problems disappeared when using Bluetooth. I hope this helps someone.
Again, I DO NOT own the Xbox One Wireless Adapter for PC. I am only using Bluetooth.
I have an Intel 9260 WiFi card on a PCI Express x1 adapter which I use to connect to the internet and it has BT 5.0 which I have been using for a few weeks and it seems to work well with everything.
BT 5 is new but hardware is surfacing now and it should mke life easier.