You can check it in PageSpeed Insights https://developers.google.com/speed/pagespeed/insights/ it is located in the Diagnostics section and has the name Minimize third-party usage. Usually, the Third-party code blocking the main thread for the XXXX ms parameter is also indicated, and if you open it, you can see a list of third-party resources that affect the loading speed.
How I do it
I delay the loading of these very resources so that they are loaded only after the site itself is fully loaded. They all remain but no longer slow down the site.
Scripts from third-party resources often also affect such points in PSI (PageSpeed Insights):
After completing this kwork, the influence of these points on the speed of the site may significantly decrease or disappear altogether.
The price depends on the number of resources, so check the site in PSI and choose the appropriate extra options.