It's best not to open the cap when hot, as you discovered.
The head gaskets are not blown badly, if they are. When they are bad, exhaust gasses are pumped into the cooling system, and push the coolant out fast enough that you wouldn't have made the trip to the restaurant.
Lack of white smoke doesn't mean a lot, as that is not the most common failure mode. Usually the white smoke is a failed intake gasket.
Here is what I do to determine cooling system & head gasket condition -
During this, never open the cap.
Before every start from cold, check the coolant level in the recovery tank. If it's moved off the full mark, add some to get it on the full mark.
Sharply squeeze the upper radiator hose, and listen for gurgles and the giggle pin. Remember how it sounds, so you can compare to the next drive. You can hear the difference between air and no air in the system. A little bit of air doesn't worry me.
The real thing is to note any changes. More air or less air? Does the level in the tank change? Which direction, disappearing coolant, or additional coolant?
Run this monitoring for at least a week of trip or 2 per day driving.
Intake gaskets, or the seal under the carb or throttle body can make coolant slowly disappear. Also, they let air back in as the engine cools down.
I have seen small leaks to the outside, from slightly loose cooling system, hoses, pinholes in the radiator, seeping from a head gasket. They keep or grow the amount of air in the hoses that you check with the squeeze test, and also cause coolant to slowly disappear. If one of these leaks is onto the block or other part that runs at 190 degrees plus, there is little evidence left to find it visually.
About cooling system hoses - I use plumber's silicon grease when installing them - just a little - it makes removal a LOT easier. And seems to help with sealing - after the first drive with any re clamped hose, once it cools back down, re check the clamp tightness. Sometimes things settle in and they are loose.
The tricky head gasket failure mode is when a tiny pinhole develops at one of the fire rings, that allows exhaust gasses to leak into the cooling system. These will slowly get worse over time. It can take 6 days, 6 weeks to 6 months before they get bad enough to make the car undrivable without risk of serious engine damage. The best way to catch this before serious engine damage is to check the level and air before every drive, until you determine that things are stable. Once this starts, any over normal temp while low on coolant accelerates the failure.
At the beginning of this kind of slow leak failure, there is no other way I have seen discussed to detect it. Lots of ways once it's pretty bad, but the above will tell you before it gets bad, so you have more time to plan, and if you are checking, and refilling, you get away with it longer than diagnosing by the temperature gauge.
I have nursed them along for months using this procedure, while I resealed a spare engine. Also ran one with a cracked head for months the same way. If you are near seal level, you can also modify a radiator cap and run zero pressure in the cooling system, which makes the coolant loss slower, which is also part of how I got away with that. This is probably not a good idea at significant elevation.