Lucid Motors Inc.’s last-gasp appeal to investors succeeded in pushing through approval for the electric-car startup’s deal to go public by merging with a blank-check company.

The marriage between SPACs and clean-tech vehicle startups is on the rocks as regulators push for detail.

Peter Thiel-backed Luminar Technologies Inc. briefly touched an all-time high within days of emerging as a stand-alone company as investor excitement over developers of laser sensors that enable autonomous driving ramped up.