Inspiron 3910 slow problem

Last week my Inspiron 3910 developed a serious slow problem and I'm not sure what caused it and how to solve the slow problem.

I added the Windows 11 update on May 16 which led to extreme slowness on some websites (Amazon, Postimage, etc.), but other websites are ok.
The problem got worse, so I deleted the May 16 update---with no improvement. Then Windows 11 released another update on May 19, with no improvement. Sometimes I get a message saying there is a Protocol Error.

Two days before I added the May 16 update, my Inspiron 3910 fan was noisy, so I opened it---maybe the fan cover was loose, but the fan noise stopped. 

So, two questions:

1. Any ideas on how to solve the slowness on certain websites maybe caused by the Windows 11 updates?
2. Is it possible the slowness was caused by the fan which caused overheating?.......(I would think if overheating damaged the pc, it would slow down all websites, not just a few such as Amazon, Postimage, etc) and is there way to determine if the fan caused the problem?