Hmm, as a long-term AppleTV hardware user I have to say Airplay can be flakey at best.
If I understand correctly you don’t have an AppleTV set top box but your Samsung can accept Airplay of video content from a Mac or iPhone/iPad - either a predefined stream or screen mirroring.
Many years ago, and things may have changed, websites and video apps could specify if video content could be Airplayed or not - so you could view an item on iPad on a website or say in an iPad app but the content ‘provider’ could specify even on a per video basis if video Airplay was allowed.
If you are trying different content but managing to get sound on multiple Airplay destinations this might be the cause.
This might be something else entirely, but I have an AppleTV hooked up to a projector and even if I set it to output to my Nova rather than puny projector speakers it always seems to reset and we have to set the Nova as a destination again. I have a pair of original Apple Homepods which I’ve used until recently with the projector doing video only, for many things they sounded great, YouTube for some reason always caused issues with audio after a while, one speaker dropping out or video sync issues.
Appreciate your setup is different, just saying Airplay does not seem as robust as it should be.
More often than not if I have issues with Airplay then restarting the router and all relevant devices corrects the problem for a while, though not always. It may not be a networking issue but you may or may not have seen destinations appear more than once in an Airplay list which implies some network oddness!
The other thought depending on how you are accessing the Airplay options is that you may be in an audio only setting.
Apple also seem to do confusing things - my Homepod stereo pair are somehow linked to my daughter’s AppleTV and appear a Daughter’s AppleTV+Homepods in menus - I actually just want the Homepods to appear as a stereo pair not allied to anything else.
It really ought to be simpler and more intuitive than it is, but they really don’t care much about AV or audio as you will see from our laborious attempts to get lossless hires Apple Music to Airplay (you can’t currently).
Apologies, I’ll re-read your post again later as I may have got the wrong end of the stick, but unfortunately I have no TVs with native AppleTV/iTunes purchases playback app currently.