I'm using an older iPhone (SE, but the second version) and iOS 17.4.1. I tend to keep things as they are - minimum upgrades - until I have to make a change. Most recent update to 17.4.1 was probably a few weeks ago (required by my bank's mobile app).
The "download occ" popup started for me on Sept 19, 2014 (two days ago), using Safari. I didn't X anything, just backed out of that page. It reoccurred multiple times: nerves and stress. I re-booted my router and phone, went to MSNBC, clicked on one headline, started to read a little bit, and got the prompt again.
I'm generally extremely careful about my clicking; if I get somewhere I shouldn't be, it's usually a finger-touch error. Mostly use my phone browser for news, word games, plant id and research. I'm reluctant to download or install anything - including ad blockers. Not sure why, but no prompts since late last night, knock on wood! Just adding my specs for stats even though I don't think they reflect anything new.