I have been using a MX Master 3 (non-S), and an MX Anywhere 2S for the past few years on a daily basis, on multiple devices (Windows, MacOS and Linux). Bluetooth has been working flawlessly every time. I don't think I have ever used the unifying receiver dongle.
This is why I don't understand the DongleHider+ here. If you don't want the dongle, why not just connect via Bluetooth?
In my experience you can't use more than 3 bluetooth devices at the same time.
Currently I have a headset, a mouse and a keyboard. To add anything else I would have to remove something else.
Last year I've built a simple 3-key macro pad using an esp32 connected via bluetooth. When I tried to use 4 devices at the same time I had a pretty bed time.
I don't know this for sure, but I suspect if you have someone else sitting by you side and also using 3 devices I think the interference could cause some strange behaviour.
This is why I don't understand the DongleHider+ here. If you don't want the dongle, why not just connect via Bluetooth?