Amusingly ICAO (the UN aviation standardizations organization) has specified the ID card format for Machine Readable (Official) Travel Documents. And the passport card conforms to those specifications. But the only use of it that they officially encourage countries to accept is the Crew Member Certificate.
In all other cases, acceptance would be based on agreements between the involved countries. In theory, any country could choose to accept any such document without an agreement, but they have little reason to do so, and it is not really compatible with paper visas. Furthermore, they should refuse it if there are unmatched conditions printed on the back of the card, like the passport cards have. The result is that they are of pretty limited use, and most countries that do use them will restrict them to specific scenarios where there are agreements in place.
Not useful for international air travel but remarkably usable as general ID when traveling abroad. When I’ve been asked for an ID for random purposes and showed it while traveling, it’s worked just fine. Worth the $100 or whatever to not have to share my home address with some stranger
But it is pretty useless, I didnt renew mine with the renewal of my passport book
Can be used at bars and domestic travel and with employer verification, but not international air travel which is the main reason i would have it