“Enroll” and “enrol” are regional spellings of the same verb. Cambridge labels “enroll” as the US spelling and “enrol” as the UK spelling, so the choice should follow regional or institutional style.
“Leveled” and “levelled” are regional spellings of the same past form. Cambridge distinguishes US “leveled” from mainly UK “levelled,” so the choice is regional rather than semantic.
“Smolder” and “smoulder” are regional spellings of the same verb. Cambridge identifies “smolder” as the US spelling and “smoulder” as the UK spelling, so the choice is regional rather than semantic.
