What if you have more than 100mL of Mayo on it?
True story. My FIL tried to bring a jar of mayo through security and they made him throw it away.
Next time consider bringing all liquid condiments in separate 100ml containers and applying them to your sandwich after security theater.
OP you are allowed to bring solid foods without restriction but are still limited to 100cc for liquid/salsa/sauce even if it's sandwiched. Practically it is not strictly enforced if your sandwich looks edible, I've never had my pulled pork sandwiches analyzed.
So, technically, TSA is not being maximally strict in enforcing their rules when they allow any sandwich containing even tiny amounts of liquids like olive oil or gels like mayonnaise to enter outside the single 1 liter bag per person that also contains their shampoo and toothpaste. No, I don’t expect TSA ever to enforce this maximally strict interpretation, but that is how the rule is worded.
By contrast, some foreign airports that mention the 100ml rule make no mention of the single 1 liter (using the non-US spelling of liter) maximum enclosing container volume per passenger, let alone the requirements for the enclosing container to be a clear, zip-top, plastic bag. So this particular absurd pedantry about an absurdly worded rule that’s designed for TSA to keep you guessing on each screening about with how much leniency they choose to grace you that time does not apply to most foreign airports.
That's the theory. In practice, enforcement of the zip-top plastic bag rule is next to non-existent.