I finally managed to learn am/pm after working with brits for years, but every time they said "after midnight, past midday" as if it made it easier to remember, I just responded with "after midday, past midnight"
At least for my brain, 12pm and 12am are the sticking points.
As you note, pm is Latin for after noon, yet we call noon 12pm. Noon isn't anymore after itself than it is before itself. Neither makes any sense.
With 12am, we generally seem to think about midnight as the end of the day, even though it's really the start of the new day. The Latin isn't confusing here, but the numbers get real weird. We start the day counting at 12:00, go up to 12:59, and then reset the count to 1 an hour in? Our 12h clocks are split between being 0-indexed, and a weird variant of modulus 12.
I'm clearly overthinking things, but I don't always immediately remember which 12 is which. Latin doesn't help.
With 00 it's clear which time we're talking about, and which calendar date it's part of. It's also the easiest way to sort out which 12 gets mislabeled what.
I still have to think twice when someone says something about single digit hours and somehow mean afternoon. We even have an expression in my language for the nightly hours after midnight, they are called ”little hours”.
I remember it as the _M changes the moment it hits 12. So if the rest of the day is PM, the moment it hits 12(for noon) it swaps to PM. In the same way, the moment it hits midnight, it swaps to the morning hours of AM.
My job uses 24h/UTC time a lot. Love the 24h time, everything I can set to it that I use is on that format. Can’t set the coffee machine or microwave to 24h time.
UTC? Hate it. Too much math that changes with the time change and your time zone to get to UTC. Thankfully wearables and phones will often let you have multiple clocks visible.