When to call electrician

Grande Prairie - Kidde smoke alarms (hardwired and some battery - all interconnected) go off one morning. No smoke or fire found, can’t figure out how to make them stop, push the silence button on them all (3500 sq ft house, at least a dozen to do) and check breakers.

Smoke alarms stop… but one floor of the house has no power, flip all breakers, realize gfis on that floor won’t reset.

Replace all the gfis on that floor. Still no power. Check voltage on panel, all breakers except 1 have 240 volts, the 1 has 0 power. Replace breaker - now all breakers have 120 volts and still no power on the floor. Circled breaker is the one we replaced.

Any suggestions? Or time to call a professional?