Not to mention Trump's empty promise to these Iranians that the US would be there to support them as they protested and were summarily executed en masse.
Exactly, a recent and local demonstration of the US's unwillingness to follow through, making it an even harder sell to others in the country. Assuming awareness of it. I know with their Internet being crippled it will be harder for information to spread quickly, but it will still spread and many probably haven't forgotten the last time the US betrayed, or at least failed, them.
Some of them still remember when the US helped the UK overthrow their leader to support an oil friendly dictatorship, after they nationalized UK's oil business there
What could the West do to support the protesting Iranians outside of a full-scale invasion?
The "protesting Iranians" is mostly just Israeli propaganda.