Occupational therapy helps people do the everyday things that matter to them: dressing, working, cooking, playing, studying. OT interviews test whether you understand that focus, and whether you have the empathy, creativity and judgment to help clients pursue it.
Interview practices vary a lot. In Canada, some programs interview (McMaster, UBC, Manitoba, UQTR) and others rely on grades and Casper (Toronto, Western, Dalhousie). Where interviews exist, they can be very heavily weighted: McMaster ranks applicants 75% on interview and 25% on GPA, and Manitoba 50/50.
The question underneath every OT interview: does this person understand what occupational therapy is, and would clients feel heard by them?
In the US, most programs apply through OTCAS and many interview, sometimes with a writing sample.