This is missing the important nuance, that the allies just didn’t want certain weapons to be used on russian homeland. AFAIK it was always okay for Ukraine to use other weapons (eg. their own drones), which they did successfully, many times.

I suspect the allies didn’t want russia to be forced to develop better countermeasures against western weapon systems or didn’t want pics of German tanks on their way to moscow again. It could cause a lot of trouble for everyone.