Probbly you performed
npm install ngx-turnstile --save
and then you get output something like :
which acctualy means that you need @angular/common@">=16.0.0" above or equal 16,and as i can see you are using angular 15,
then you performed npm install ngx-turnstile --save --legacy-peer-deps
and you imported import { NgxTurnstileModule } from "ngx-turnstile";
in modules and after you get your error.
Here is working example with angular 19 : https://stackblitz.com/edit/stackblitz-starters-l9unkwij?file=src%2Fmain.ts