Does it require a phone number, or just prompt for it? From what I've heard, it always has a field for a phone number, but it sometim es lets you submit without one (based on some sort of not-a-bot trust score, ReCAPTCHA v3 maybe?)

Required, couldn't proceed through account creation without it. At least when I tested it just now that was the case.

you can actually create gmail accounts without phone numbers

For me in Russia gmail always requires a phone number. But my ISP is large and maybe someone of its users was sending spam or did something bad.

There are ways to create Gmail accounts that don't require phone numbers.