Tyre repair with patching fungus

Hi all, I drove a little nail into my rear wheel some time ago, as a result of which there was constant air loss already after short distances. Since the tyres are not very old, I decided to go to the workshop of my trust (since more than 10 years) before spending money on new tyres. “You don’t need a new tire, we will fix it immediately.” Said, done. The repair lasted a maximum of 10 minutes and the tire was patched with a “pilt”. The air pressure on all 4 tires was checked. Cost point 16 EUR. “Your tire is now fully functional again, you can easily drive up to 200 km/h with it.” At home I looked at the whole thing more closely. For me this repair with the fungus looks somehow very unprofessional. Instead of the nail it looks like I was driving into a blue chewing gum, and that’s how this mass feels. Now my question: Does someone have experience with the can I trust the workshop if they tell me that the tyre is fully functional again? I drive to 80% city and country, but if I’m on the highway I don’t want to take any risk, especially since the affected tyre sits on the rear axle, which will not go well with a tyre pitcher or the like.