The values within a checkboxes field are stored within a single semicolon-delimited string.
apple;orange;pear
So you can use [Contains] "orange" as long as there is no possibility of confusion among the values.
To prevent confusion I recommend having another field that has an extra semicolon at beginning at end/
;apple;orange;pear;
This field can be populated using a Change Data Value step. Then you use [Contains] ";orange;".
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