Despite my building existing for over 10 years, putting in “flat number, building name” into that system will be rewritten to “house number, building name road” which is an address on a he other side of town (and London ain’t exactly small).
I’ve had multiple orders go missing as a result.
The only universal address input is a freeform text box. Optionally with a country, which should also be a freeform text box because countries get created and destroyed and you won't remember to update it. City or district is probably okay - as a freeform text box - addresses without one can write (no district). But street addresses are different everywhere and must be freeform unless you're the government of that region.
More concretely, a postcode is usually specific to between 7 and 30 dwellings, in the usual case it's about 15 houses.
Contrary to common belief, they're not always on the same street, but in the vast majority of cases (like maybe 99%) house number + postcode is sufficient. Definitely flat number + building name/number + postcode should get your stuff there.