After i Updated my Mac to Catalina10.15.7 my wifi is running slower 1000times.

We need information.

Please run Etrecheck and post its full report here.

Use the “additional text” button and paste the report into the text box.

Also did you restart your mac and your router?

You have a bunch of probable adware. Run Etrecheck again and follow the instructions to remove it. Then restart your mac and see how it goes.

I have one observation to offer. The computer only has 4 GB of RAM installed which is woefully insufficient. To run Catalina, the minimum amount of RAM should be 16 GB or more. Catalina does use more RAM than earlier operating systems. I think part of your problem is the lack of RAM which is causing the computer to function very slowly overall.

I agree that 4GB of RAM is not a lot, but:

a) it would not specifically affect wifi speed so excessively

b) 8GB would be more than enough for most people. More RAM only makes a difference if you use more demanding applications or have a lot of them open at tge same time. If one is, say, just using the mac for surfing the web, checking e-mail and listening to music (all at the same time) there will be NO difference between having 8 or 16GB.

Look, I do have 16GB but I can run Final Cut Pro and a dozen other applications simultaneously. Just saying that more RAM does not a faster mac make (unless it was lacking in the first place).

In this instance, I am speaking from personal experience. My wife had a late 2009 iMac with 4 GB of RAM. She kept complaining how slow things were. It wasn't until I sat down at her computer and used it that I really understood . It was virtually unusable for anything. At the time, I didn't think to check the RAM and I incorrectly concluded that the HD was dying. We bought her a new iMac. Incidentally, I recently pulled the old computer out of the closet, added RAM and now use it for another purpose and it still runs great.