ISO 10191 . Passenger car tyres — Verifying tyre capabilities — Laboratory test methods.
This standard applies to all tyres used on passenger cars. There are specific tests for tubeless tyres, but no tests specified for the use of tubes in tubeless tyres.
Tubeless tyres are not designed to use with a tube. They also don't test tyres filled with expanding foam, but I'm sure someone somewhere has used that on a road vehicle.
There are circumstances where you might fit a tube.
Avon tyres do have recommendations for fitting tubes to tubeless tyres, but it talks about 'appropriate use' and seeking professional advice. I don't think fitting a tube with a tubeless wheel/tyre is appropriate use. It also says tubes should never be used to repair a puncture in a tubeless tyre.
An interesting bit I found:-
" When a tubeless tyre is punctured, the penetrating object is gripped by the inner liner (the built-in tube) and thus air loss through the penetration will be gradual. By contrast, when a tube type or a tubeless tyre fitted with a tube is punctured, once the tube is penetrated, air loss will normally be sudden. In this case, air will rapidly escape through the valve hole in the wheel and between the tyre beads and the wheel which, with a tube fitted, no longer provides a hermetic seal. Sudden pressure loss in a tyre can result in the bead dislodging and a loss of vehicle control. "
I suppose a similar argument exists for the use of after market tyre sealant in a passenger car. Is that 'legal'?