Which Android though? AOSP doesn't have ads. But Samsung phones are full of ads for their own and other's services (McAfee VPN, McAfee security scan, OneDrive, etc.). I heard that Chinese phones are similar. Even Pixel pushes Google One in places.
The primary exceptions are GrapheneOS and Lineage, but it's not like people can buy a phone with them in the store (yet).
I have used several models of Sony Compact phones, until Sony discontinued that line of products, then ASUS phones.
No ads on any of those, and moreover I never had and still do not have any Google account.
The only problem that I had for not having a Google account was that one of the banks with which I was working terminated their on-line banking and replaced it with a smartphone app. That would not have been a problem, except that they refused to provide the app directly for download, but only from the Google store, which cannot be used without a Google account.
I have had until now 4 Android smartphones, which did not have any ads whatsoever.
Like other posters have said, if you do not buy the phone directly, but subsidized by some carrier, then it might come with crap installed on it.
Of course, currently Google appears to make efforts to make Android worse, so it would not be surprising if ads would appear.