I would say British English seems to adhere to English grammar books that I learned in school more than American English.

For example, I was taught that we use present perfect with "ever" because the time is unspecified or something which happened in the past which is important now.

See the Cambridge Grammar say:

Present perfect simple: uses

We use the present perfect simple to refer to events in the past but which connect to the present.

We often use present perfect for talking about something which happened in the past which is important now.

we often use general time expressions like ever, never, before, in my life, so far, up until now with this use of the present perfect simple:

We often use ever, not … ever and never when we talk about experiences:

Have you ever tried to write your name and address with your left hand?

American English

In American English the past simple is often used instead of the present perfect simple, often with already and yet.

American English Did you eat (yet)? Did you finish (already)?

British English Have you eaten (yet)? Have you finished (already)?

Have you ever watched the film? ( we use present perfect because we don't know the time the that person watched the film or the specific time that that action happened is not important or its result is important now, ie I just want to know if you have watched it, the time is not important)

But American people will say:

Did you ever watch the film? (I feel strange when hearing it, why would the asker want to know the specific time right at the beginning)

Is that how American people say daily? or American grammar is not as strict as British English?