See https://help.ui.com/hc/en-us/articles/18930473041047-Best-Practices-for-Sonos-Devices and https://github.com/IngmarStein/unifi-sonos-doc - good luck, you’ll need it.

I have read those and they don’t directly answer my question although connecting Arc via wifi and then sub wirelessly seems to be safest option.

Or am I just looking for troubles with Sonos and Unifi and should look to other products?

I may have understood wrong, apparently Sonos Sub needs a wifi network to connect to Arc (no direct connection then) so safe option would be to connect both via wifi.

The Sub does need wifi but reverts to the Arc to use the dedicated 5Ghz connection Sonos uses for this purpose. The Sub does however receive an ip adress from your router, even while the Arc is “in the middle”.

I use Ubiquiti, along with others in the Community. If you wire multiple SONOS units to a Ubiquiti switch, make sure that it is set for STP, not the default RSTP.

I would prefer wiring at least Arc (some say wiring only one works) and connecting sub via wifi but ultimately seems safer to connect both Arc and Sub via wifi.

Sonos is my first option to get but I don’t like the fact it may mess my network so have to consider others too.

I have no issues with a wired Arc and a wired Beam, in another room, both connecting flawlessly to both Sub and Surrounds.

Have a few other Sonos wired where it was easy and several on SonosNet where wiring wasn’t easy. No Sonos WiFi only speakers though.