First of all, having had t do a major stringer repair, what you are showing wouldn't scare me. It may or may not need to be addressed, but if it does, it's a pretty straight forward job.
Here's what I'd do - get a buddy to come over and tilt the engine up about halfway. Have your buddy put pressure up and down on the lower unit while you watch the cracked area for movement.
If these are just gel coat cracks, you won't see the area flex much and the gap/crack won't get much wider. Keep in mind that gelcoat doesn't flex and can crack simply because it is applied too thick or because the area under it flexes more than the gelcoat can allow, but the flexing is normal for the fiberglass underneath.
If you have a serious problem, you will see those cracks widen when your buddy puts pressure on the engine. As you have your buddy do this, keep in mind how much pressure that engine is creating when you are running (downward pressure from your buddy) and how much pressure would be applied if you go hard aground at a moderate speed. Increase your pressure each way slowly until you roughly match that level of force.
I would DEFINITELY use this time to explore the rest of the hull for cracks. Look around chines, lifting strakes, areas under stringers, etc. Get a camera and video everything as you go, take pictures. Later, these can be useful comparison points to see if any cracks you find are growing.
This thread may help you know what to look for - this is probably worst case scenerio and I learned a lot.
Here's the cliff notes version of what's going to be addressed here - if you want to wade through the original thread from the beginning, start here: 1) I bought this boat sight unseen in November of 2016. The boat was nearly pristine and had clearly been babied it's entire life. Hardly a scratch...
www.mbgforum.com
In your case, I would say you can sleep well. Unless you find a bunch of other major cracks, you probably don't have an issue at all, and if you do, it's a simple thing to have fixed since it can be done from the outside and without removing decks.