..Jaeepps..
Had noticed random google sponsored ads, in browsers; with popup
login prompts, to one or another of my gmail-named email accounts.
My answer would be to avoid logins from any of those prompts from
web pages; try to triple check google services, where you may (/not)
find something to toggle, or fix this symptom. Where web content is
not needed nor desired, close those browser windows. You also may
consider clearing cookies; or alternatively re-set browse security.
As most my access might be through web-mail and browser security
is highly desired; I'd be lax with older Apple devices, if not proactive.
A newer iPhone could use Google's gmail app; those are adequate;
or when other Apple systems are older; or if webmail is often used.
[This happens most often while researching ASC topics, and see
reddit &/or other suggestions, w/ browser search. +Although use
duckduckgo; sometimes not by first choice.]
I use third-party browsers, Firefox/ESR, Brave; and if viable, Safari.
As security updates further stretch older systems, be wary/aware
of these factors.. [Your mileage and driveability may vary.]