Fresh install of Catalina knows my wifi password

How did Catalina connect to my wifi?

The WIFI connection info was stored in your Mac's NVRAM.

I ran into this same problem when I installed a couple of new (refurbished) iMacs last month. The vendor had wiped/reinstalled Catalina but had used his WIFI network in the process. In the end, it turned out the WIFI network settings were stored in NVRAM. I cleared the NVRAM and finally got rid of it.

Here's the full discussion about the experience -> https://discussions.apple.com/thread/251293807

See this article on how to clear the NVRAM -> Reset NVRAM or PRAM on your Mac.

I really have to credit Etresoft for giving me the clue about this.

Apr 21, 2020 8:43 PM in response to MartinR

It seems that this information is stored in nvram. However, it is stored in secret areas that you can't normally access using the nvram command.

https://apple.stackexchange.com/questions/195775/how-to-prevent-storing-the-wifi-password-on-the-recovery-partition

Very likely picked up the information from your Apple iCloud account. You may notice all of your Safari bookmarks filled themselves back in, too.

Thanks for that info, MartinR. I've seen more than a few people ask this question, but until now, no one in the topics I saw knew where it was coming from.