I think the HDFury Arcana could work:
https://hdfury.com/product/4k-arcana-18gbps/

You should also ask the HDFury community on Discord:
https://discord.com/invite/yCRdfPw

So, if I were to purchase this, I would plug the Xbox directly into the eARC port, and the Sonos into this and then this into a normal (non eARC) port? 

The Xbox would connect to the HDMI IN port of the Arcana. The Arc would connect to the eARC OUT port of the Arcana. The Arcana would connect from the HDMI OUT port to the TV’s HDMI eARC port. See diagram below.

I would confirm all of this on the HDFury Discord community before you purchase the Arcana.
 

The Xbox would connect to the HDMI IN port of the Arcana. The Arc would connect to the eARC OUT port of the Arcana. The Arcana would connect from the HDMI OUT port to the TV’s HDMI eARC port. See diagram below.

I would confirm all of this on the HDFury Discord community before you purchase the Arcana.
 

 

Unfortunately they informed me that this device isn’t capable of passing through 120HZ in 4K video, so thanks for the attempt. 

Why does the Sony only support 120Hz on one of its HDMI ports? What model # is this so others may find this thread in the future and maybe avoid buying this model?

It supports the 120HZ at 1080P on all of them, but on 4K only the one port. It is the 950H 65” Sony 4K TV. 

rtings doesnt indicate any limit on 4k on the one port, though it does list other limitations of the TV on the Xbox. https://www.rtings.com/tv/reviews/sony/x950h

I think this sort of limited support on HDMI inputs is rather common on TVs unfortunately. The highest quality port is usually with one with ARC/eARC capabilities.  If you’re using an AVR where video is going through the AVR before going to the TV, that makes perfect sense.  Of course, Sonos doesn’t process/pass through video, so it doesn’t make sense.  My understanding was that the entire reason for ARC/eARC was so that you would not need to pass your video through your AVR, and thus the AVR would not be a bottleneck for your video quality.

Maybe 5 years ago, but on a 2020 TV there is zero reason for only one port to support 4k. What is still common is advanced features only being available on a single port, and I think the OP may have conflated these two issues. Also rtings claims the TV cannot do 120fps except at 1080, so either rtings is wrong, or the OP is confused.

There were only a few TV’s in 2020 that had more than 1 port support 4k at 120.  I bought the LG Nano 99 series 75 inch and all 4 port supported 4k at 120.