Any and all stats of "new websites on the internet" stopped becoming meaningful 10-20 years ago, since it became trivial to generate websites. I can write a script to generate 1M "websites" as subdomains Yet a single Instagram page can be more visited than these "1M websites"

Because of this, there is no reliable stat on what the "number of new websites per month" is. To do it, you need a crawler that looks at any and all new domains and subdomains. You could do it, but it's pointless to do so. Again, because so much of it is junk to start with!

(Google or other crawlers are probably the only tools that can get this data of 'new sites crawled we've not seen before' Then again, even Google might not even bother crawling some sites that is predicted to see 0 visits during its lifetime from their search engine... and is not even useful for their AI training thanks to being AI-generated slop)