Questions about Denon Avr-X4300h

Nope, I don't. Swisscom Tv, PS etc all work perfectly.

I use the same configuration with an LG OLED65B6V. I had to set the sound settings on the TV to Automatic, then Netflix shows me 5.1 sound tracks for most content, which the receiver also receives. By the way, my TV cannot transmit Atmos via ARC. Is the sound from the TV output on the receiver when you use sources other than Netflix (e.g. cable TV)?

No, you should never put another device on top of a receiver because of the heat.

Monster HDMI Kabel, teuer aber sehr gut MONSTER Black Platinum (1.50m, Premium, Schwarz)

The x4400 has Auro3D ex works, the x4300 only has it as a chargeable update!

I recommend Oehlbach SPEAKER WIRE SP25 (mini coil, 20m, copper, 2.50mm²). Good quality at a reasonable price. Oehlbach SPEAKER WIRE SP25 (Mini coil, 20m, copper, 2.50mm²) https://www.galaxus.ch/de/s1/producttype/lautsprecherkabel-1453?opt=v9-11319:0.0000025&tagIds=77-533

Yes, it is possible, I have made an 11.2 system, you can also radio in other rooms via network. There are different speakers from Denon, Internet Radio IPhone Ultra hd also works great. So there are up to 3 zone arrangements for speakers, a maximum of 11.2 speakers can be connected. But the front speakers should be connected to another power amplifier. Up to 9.2 there is no need for an additional amplifier, but you should make sure that they all have the same Om number.

Sure, it will. But why would you want to buy such an expensive Receiver then...

Zones 2 and 3 can be switched on and off via the HEOS App. In the HEOS App, a link to the AVR Remote App can be selected where inputs (not HEOS zones) can be assigned to zones 2 and 3 and the volume of the zones can be changed. However, the AVR-X4300H only has 1 HEOS zone, which can be played on either one or multiple AVR zones.