I don't believe tics aren't related to anxiety - my personal experience is that they are.
I never noticed DDs tics until lockdown, when they exploded (DD had noticed and tried to tell me, but I didn't understand) She now has a diagnosis or Tourette's, although you wouldn't know if you met her today. She can suppress her tics, but they will come out when she gets home, or she's around me. Initially I thought I was making her tics worse, but apparently it's because I'm her safe person, and she can just let it all out with me.
I wouldn't have thought DD was a nervous child, but I now realise that anxiety and tiredness are the two things that will trigger her tics. I also try to make sure she isn't deficient in magnesium - easier said than done with a teen who thinks they know best.
It could be that your DC grows out of the tics, or that they get worse during puberty and then calm down ,which is what seemed to happen with my DD. There is very little help for parents of children with tics - DD received a diagnosis of Tourette's and was discharged on the same day. The Tourettes Action website is amazing though, and have lots of fact sheets you can print off and pass on to school.
Ignore the tics as much as you can - I know that's really, really hard!