Who is responsible for the fall of the underground garage in the commercial street, the developer or the property?

See whose responsibility it is. Commercial garages generally belong to developers and will entrust property maintenance. Improper maintenance or maintenance without warning signs must be responsible.

Of course, if you are in a clear position and have full capacity, you should have self-judgment and estimate that you are partly responsible.

Better have evidence, witness lights.

It's best to negotiate first. For myself, the prosecution time is too long, and I have to toss and turn if I get hurt.

I hope to give you a reference.