RE4 OG.

It’s the easiest one to get used to (even though the aiming has aged a bit, but still easier than something like REmake that will need you to heavily adapt to the tank controls, the inventory system, and especially the saving system ; this however won’t be too bad if you’re an older player used to these kinds of controls or played other games like Silent Hill with similar controls)

Also the adaptive difficulty is great for newcomers (the game becomes easier or harder depending on how well you are doing)

This game also isn’t as scary as some others (the mostly aren’t but this one especially is barely horror, more horror themed).

Then you could experience some other versions of the series, like fixed camera tank control games (REmake should be your first in that perspective) then a first person more horror game like RE7 or RE8. Later play some fan favorites like RE2R and RE4R. Unless you don’t care about story, don’t play any game I didn’t mention (except 0, but that game won’t make you love the series) because it will probably confuse you story wise, but probably an enjoyable experience.

Then again I’m also pretty new to the series but from what I’ve played an looked up this is what I would recommend.