As far as I know there aren't any CPEs (customer premise equipment, read: routers) devices that can NR CA at the moment.
Only newer mobile phones, such as Mi 11 Lite 5G which is based on the new(ish) Snapdragon x53 modem can NR CA.
I assume chipsets released from 2021 onwards are the ones that could potentially be capable of NR CA.
Correct, it'd be n78+n78, since the blocks they own are separate so they couldn't use it as contiguous 140Mhz bandwidth.
700mhz is n28. n78+n28 NR CA has been seen (on the Mi 11 Lite 5G I mentioned above), though not in the UK (yet)