I use a FLIR One on Android. I've charted internal leaks (where cold air blows in through cracks) and external (where heat escapes through eg old windows).
Wait for a cold day (eg 0C), heat the house, investigate everything you can. My 1930s London house has SO many leaks, I've spent 3 years slowly fixing them.
I have a talk I should give on using 12 Govee hygrometers to back-calculate moisture (absolute humidity) coherent per room, as I was charting moisture loss to trace air leaks.
How did you use the thermal camera exactly? Any tutorials on that?
I have a garage, and I had issues with using the thermal camera - if the building materials were not uniform they reflected/radiated IR unevenly. It could show a piece of uninsulated area as hot and very well insulated as cold.
Get some wash-off spray-on chalk (essentially spraypaint that won't survive the next rain, because it's made to disappear when hit with rain/a hose). That should give you sufficiently uniform surface emmissivity to deal with those problem spots.
Industry standard in HVAC is to use a door blower to provide positive static pressure and then use a fogger. It works quite well since you have a direct visual indication and are not deriving loss from a secondary observation (temp/humidity).