To add to this, I would argue that ikigai can be directly translated to purpose in English. Sure purpose has additional meanings, and ikigai has a philosophy behind it which one word like “purpose” does not convey, but if you use purpose in a sentence that has something to do with how you find meaning in life and a reason to go on, then people will correctly understand your meaning.

If purpose is not good enough then try “a reason for being” “a reason to live” etc

Maybe people are confusing describing a whole philosophical concept with translating a word