I think it also depends a bit on the situation.
Sometimes I meet friends and I'm in a bad mood, and showing it and talking about helps me. In that case, my friends are more than willing to share my worries and to discuss it.
Sometimes, I feel bad but feel like meeting a friend might make me feel better. Then I have 2 options: 1st, I try to play over my bad mood and act cheerful, hoping that it will lead to me feeling actually better (which can absolutely work! Sometimes you need a little push to stop dwelling on something). 2nd, I go but tell my friend that I don't feel too well and whether we can just do something low-key together, like watching a movie. I don't suppress my bad mood altogether, but I also don't shower my friend with it, but don't force myself to be unnaturally cheerful either.
And finally, sometimes I feel bad (or not even feel bad but my social battery is just empty) and I honestly don't want to see anyone. Then I don't. I try not to cancel too much because of this but instead try more obtion 2B (doing something low-key) to keep in touch with my friends, but I absolutely do this, too. If you have good and understanding friends, it shouldn't be too much of a problem.
If the people I'm meeting aren't my friends but looser acquaintances, I'm more radical between "do I feel well enough to see them or would it cause a meltdown", and I decide to go or not go, feeling less bad about it. Everyone should understand if you say, sorry, I had a bad day, I will join again next time.
Since I'm practicing to be fairly honest and usually meet nice people (like my DnD group e.g.), I got into the habit of being open and of letting them know beforehand when I'm really feeling a bit low or my social battery is on limit but I still want to go. The fact that they know already feels like a relief, and I know that it will be okay if I don't talk much or zone out, without having to explain.