If you can raise the TV a bit a Sanus mount shown in the link may work.
https://www.amazon.com/SANUS-Soundbar-Mount-Designed-Sonos/dp/B08KJDQBSW/ref=mp_s_a_1_1
The only other option (IMO) are 3rd party outboard speakers on stands powered by a Sonos Amp. However they will be lower than the TV. Although the lower position may work to your advantage to place the speakers at ear level 🤔.
You can still use Era 300’s as surrounds and a Sonos sub. However, there will be no Dolby Atmos sound as with the Arc Ultra. The center channel will be a Phantom channel created by the outboard speakers. * Click the link.
Others may suggest alternatives but I’m not going down that rabbit hole.
https://www.sonos.com/en-us/shop/amp
Mounting the Arc Ultra above the TV can be done but as your research shows is not ideal.
* If using 3rd party speakers with a Sonos Amp an alternative to Era 300’s as surrounds would be Era 100’s as IMO they are a better match. The Era 300’s could be repurposed as a dedicated stereo pair for music.
Also, sending TV audio to speakers not part of the home theater setup is not recommended as there will be a 75ms delay causing an echo effect.
Together Everyone Achieves More = T.E.A.M.
