A HDMI switch would solve sound dropouts?

Which issue? A switch would certainly solve the ‘not enough HDMI inputs issue’ , but would unlikely have any change at all on the dropouts. 

I don’t need more HDMI ports, I just don’t understand why I have sound issues when all of the devices are connected to the TV.

The Sonos, in general, plays what it is handed. If it’s working in some situations, and not in others, I’d be checking the devices feeding the data, no matter what they are, as well as the device passing the data on to the Sonos. There could be differences in various settings, and there certainly are different HDMI cable types, some of which appear to cause difficulties. And a Sonos only provides one when you purchase a soundbar, not one for each device you want to connect to the TV set. 

Based on the scant information in your post, I’d certainly be checking the LG for updates, then the settings on the TV set for audio, and the settings for the PS5. 

Unfortunately, Sonos merely respects the ARC and eARC standards based in CEC, and doesn’t control the CEC signal from your TV to other devices. All it essentially does is report to the TV set that it is an audio device, and can handle X formats. It’s the computer in the TV that handles all the other things, including which formats it receives (and sends on), and other issues. If CEC isn’t set up properly on all devices, there”s not much the TV set (and the Sonos, as an audio sink) can do about it.