Which TOCs still do not use RTT, then? They're getting fewer and further between now.
I'm assuming that you mean "that don't participate in Know Your Train" rather than "that don't use Realtime Trains".
If so, the Train Operating Companies that don't participate in Know Your Train are:
No allocations
Arriva Rail London (London Overground)
Eurostar
Allocations shown (I think these are pretty recent)
Govia Thameslink Railway (Thameslink, Great Northern, Southern and Gatwick Express)
Merseyrail
Southeastern
==============================================================
The Train Operating Companies that
do participate in Know Your Train are:
Avanti West Coast
c2c
Caledonian Sleeper
Chiltern Railways
CrossCountry
East Midlands Railway
Elizabeth line (that must be pretty recent!)
Grand Central
Great Western Railway
Greater Anglia
Heathrow Express
Hull Trains
Lumo
London North Eastern Railway
Northern
ScotRail
South Western Railway and Island Line*
TransPennine Express
Transport for Wales**
West Midlands Trains (West Midlands Railway and London Northwestern Railway)***
*The 28 Class 458/4s are still "Allocations only" for some reason
**The 24 Class 756s are still "Allocations only" for some reason, 11 months after entering service 
***The 3 Class 150s are still "Allocations only" for some reason