Want to buy first real bike and possibly use it for a sprint triathalon

Haven't ridden a bike since I was a teenager but now I'm 33M and have a 4yo daughter who is slowly learning to ride a bike and I want to be able to take her on rides together. We would likely be biking on asphalt paved paths in parks around town as well as some smooth gravel nature trails we have nearby. I've also recently started working out on an exercise bike 3x a week to improve my heart health and am considering signing up for a sprint triathalon next summer, so if whatever bike I pick up is capable of completing that (not going to be too worried around speed/time) then that would be best.

I'm 5'8" and my inseam is around 30.5". I stopped by a local bike shop yesterday and a size small Giant Escape seemed to fit right.

I'd like to pick up something used so I don't have to invest too much right away into something that I don't know how much I'll use. I'd like to stay around $250 or so, but could go up a little more if something is

I have initially been looking at hybrid bikes that have a rigid front suspension because they feel like a good balance of being light enough, capable in most conditions I'd use it, but also comfortable for someone just starting out. I am not completely against getting an actual gravel bike but I don't know much about them or what models I should look for.

The specific models I have been considering have been:
– Giant Escape (size small)
– Trek FX (size Medium?)
– Specialized Sirrus X (size Medium?)
– Cannondale Quick (size Medium?)

This Trek FX 7.2 is available local to me for relatively cheap but it seems like an older model. I also am not sure if this would fit me, as the Trek sizing guide online recommends a medium and I'm not sure how that corresponds to this being a 20" size.

Would you recommend this particular bike, one of the ones I was considering above, or a completely different type of bike like a gravel bike for what I'm looking to do? Thank you in advance!