Ok I tested this on a t8 mini running google chrome.
the box to select device is not greyed out - But it does not allow entry of the device type.
However, the list presented only has supported proprietary boxes in it, like Apple TV, Roku etc.
Clearly, android tv boxes Are not supported and hence the device type is not displayed.
This is pretty consistent with uk media apps like sky go, sky sports and BT sports etc.
There is an nbc apk in the Google play store (you may need a VPN to see it) but I bet this is restricted on android boxes. There used to be an nbc sports addon on Kodi but I don't think this is maintained any more as nbc changed their authorisation method. Maybe you could search for info on that.
So in conclusion, I don't think there is anything wrong with browsers running on the t8 mini.
As a matter of interest, on the android boxes where you say it is working, what device type did you select?
****update****
You may be able to get nbc sports extra via Kodi provided you have a subscription (and may need a VPN)
https://seo-michael.co.uk/how-to-install-nbc-sports-extra-live-for-xbmc/
It is also worth seeing if the nbcextrasports app from Google play does actually work. (Again a subscription is probably needed plus VPN)