MacBook Pro trackpad stopped clicking

On anything from the last several years the click isn't a real button, it's a vibration motor faking one. So if the Mac is frozen or the trackpad has lost power, it feels dead solid - restart first and see if the click comes back. If it doesn't, look in System Settings > Trackpad and check the click pressure setting hasn't been changed, and turn on Tap to click as a stopgap. The one to take seriously: if the trackpad sits slightly raised, or the bottom case looks like it's bulging, that's the battery swelling up underneath and pushing on it. Stop using it and get it to a repair shop, don't keep pressing on it.