“Having run into this problem on Airtable before, I thought — could I build this for this new platform that's taken off?… I kind of validated it by looking at their forums to see what problems people were running into.”

Mine the host platform's forums — repeat painpoints are your validation signal

Validation doesn't require surveys or cold outreach. Pair a pain you personally hit with public evidence of others complaining about the same problem on the host platform's forums. That's enough signal to start building.