Cannot access many sites, Google gmail and youtube work

I cannot access many websites over wifi on a 2 year old Dell laptop on my home Comcast wifi. This problem started slowly a few months ago, and has slowly got worse.

- I can access all websites on the same laptop at work

- I have a Mac laptop that can access all websites on the same home network

- Xfinity have replaced the modem/router

- Common error messages while using the PC laptop include timeout errors, connection reset errors, etc.

There are similar issues posted elsewhere on this forum. For example:

https://forums.xfinity.com/conversations/your-home-network/help-most-websites-not-loading-google-youtube-facebook-load-most-others-do-not/65404ba177679f48f5bc578a

Any help appreciated. Thank you!