What if technological progress stagnates and we never achieve AGI?

Short term, nothing much. Long term, aliens arrive and we become slaves (or some other avoidable X-risk)

The future lightcone becomes a bit less awesome

The assumption is that AGI would be a very useful tool, as it would be able to do things (invent, coordinate, control, etc.) that base humans cannot. If it turns out that AGI isn’t possible, then that would greatly limit (or slow down, which amounts to the same thing) the pool of other possible things to be done/created/made.

What if steam engines weren’t invented?