Although I don't know for sure, I doubt it. The Iridium radio obviously does not interfere with the GPS receiver in the inReach devices. And your fish find sonar does not interfere with the GPS receiver in that device. So I would not a expect the two devices to interfere with one another.
Unless somebody here has experience with this, you'll have to call tech support to get a definitive answer.
You can use a Garmin inReach device alongside a handheld GPS or marine chartplotter without issue and shouldn't experience any interference. In fact, the inReach Mini is sold in a Marine bundle which includes a powered mount you can install on your boat. The inReach Mini will even pair to certain Garmin chartplotters which allows you to interface with the inReach Mini from the larger screen of the chartplotter. For more information, reference Pairing the inReach Mini to a Garmin Marine Chartplotter.
