Reports have it that interestingly, Switzerland, which is not a part of the EU, has been spared of this rule for its airline Swiss. As such, people travelling going from India to the UK on one-stop flights can do so via places like Switzerland and the Gulf, without requiring a transit visa for these places.
If reports are to go by, non-EU citizens can, however, fly to the UK without a transit or regular Schengen visa only through non-stop flights or by one stop flights only through Gulf countries or Switzerland.
As per the airline officials, the updated change has been in place since the middle of the pandemic from January 1, 2021. And during that time, India had a bubble system for international connectivity with stringent conditions on which nationalities were able to travel by taking one-stops. So at that time, travel between the UN and India happened mainly on direct flights or via places that did not strictly follow the no-transit rule for Indian travellers.