@vitreouschain, I’m pretty sure you are locked in to the tyre you qualified on, unless you miss the top 10, in which case you have free choice. It’s modelled on real life, certainly within Career / Quick Race modes this is the case.
I think it would be for online too, as it’s not a difficult thing to code. Also it would probably more work to make it non-flexible in some modes and flexible in others.
Anyway, long story short. If you qualify and do your fastest lap on option, you have to start the race on that tyre if you finish in the top 10. If outside top 10 you still have free choice. If you don’t post a lap you get free choice.