jstests/core/timeseries/query/timeseries_out_non_sharded.js and jstests/sharding/timeseries/timeseries_out_sharded.js currently strip fixedBucketing from the expected output collection options unconditionally, to tolerate FCV-changing suites where the field can appear or disappear mid-test. In stable FCV suites, the field should be assertable: absent for legacy timeseries, true for viewless timeseries. Add the appropriate assertions gated on stable FCV.