Will I be able to use Stratus 3 with different flight bag apps simultaneously?

Yes, as long as those other apps are all supported on the Open ADS-B (GDL90) protocol.

For example: Stratus 3 can be sharing ADS-B data with FlyQ and Stratus Insight simultaneously. This does not apply to ForeFlight, because ForeFlight Mobile uses its own ADS-B mode.

For example: Stratus 3 can be sending ADS-B data to ForeFlight only when in ForeFlight’s ADS-B mode, but not any other apps simultaneously.