Your Arc can only play/process what is sent to it. No Atmos in: no Atmos out. 

@nik9669a 

I was thinking if there was a way to come around the TV being the issue as the PS5 itself should be able to send an Atmos-signal

You could get Atmos in from external sources like (possibly) you PS5 by using a HDFury Arcana or a Feintech VAX04101. 

FYI… the PS5 only supports Dolby Atmos audio on Blu-ray and UHD discs. It does NOT support Dolby Atmos on streaming apps. And as far as I know, it doesn’t support Atmos on PS5 games either.

If you plan on getting the Arcana or VAX04101 and you want Dolby Atmos audio from streaming apps, consider getting a Roku Ultra, Apple TV 4K, or Nvidia Shield.

Update:

Hidden amongst all tv settings I found some alternative that was switched to PCM. Changed that to “pass-through” and now we have Atmos streaming. Not just from the PS5 but from the tv’s internal streaming apps as well.

Good that I didn’t buy a new tv directly

Are you getting Dolby Atmos audio from the streaming apps on the PS5? If so, which apps?

No I got it from the tv’s streaming apps, so Disney+ and Netflix. 
not sure why the tv says it doesn’t support Dolby atmos but at the same time can have the signal sent to the Arc.