They self propagate like you say (but humans also spread them around). Bananas have a near zero rate of sexual reproduction, if you can get one to produce a seed, it's viability is low.

If you can get the seed to germinate, the resulting "offspring" from that will be distinct from the original banana, a new variety. It will not necessarily be "true to seed". It might be a better banana, or worse.

If you plant a lettuce seed you will get the same lettuce, year over year. Same with peppers and tomatoes, etc. Their traits were bred instead of cloned.

You "might" get the same pepper, lettuce or tomato. If the parent was non-hybrid or open pollinated.

If it's a lettuce, pepper or tomato from the grocery store almost for sure it's a hybrid and you won't get the same plant as the parent.