Do you have to be serious to be professional? I sure hope not. Life is too short to keep a straight face for eight plus hours every workday. But there are ground rules: Keep it short, keep it consensual, don’t bother others, and know your environment.
I brought in pool noodles at a previous job, because it is impossible to stay in a bad mood while fencing with pool noodles. We had big personalities on the team and meetings would devolve into hurt feelings and raised voices more often than they should have; having a silly physical outlet definitely helped release the tension afterwards.
We took our pool noodle fencing outside or into the cafeteria, where the noise wouldn’t carry into working areas. We made sure there weren’t external people around. We kept it to ten minutes maximum, because did you know pool noodle fencing is also a great physical workout?
It’s a cliché in the tech bro startup world that the office has Nerf guns, and there’s a certain type of personality that thinks surprising someone who is busy working with a Nerf dart to the shoulder is a good idea. It is not. They’re working, and you’ve just interrupted their train of thought. Are there others in the room? Nerf wars etc. are fun, and they may be quick, but they are also loud and involve Nerf darts flying around. It’s not for everyone, and if you plan for that from the start and take your Nerf guns outside, you make life so much easier for people who may not share your enthusiasm for in-office pewpew.
Aside: "But it's part of our culture!" Bro, no. If you select only for people who are like you in order to make your office fun, you are missing out on a lot of good candidates for the wrong reasons. "They just can't take a joke!" They don't have to; it's work.
This is not to say that the occasional interruption of work is bad. To the contrary, sometimes a goofy break is exactly what you need, and that time is well-spent if it allows you to focus better afterwards. But this is where “keep it consensual” comes in: as soon as someone else isn’t OK with it, you’re done, whether by taking your fun elsewhere or stopping completely.
Aside: Trying to be ridiculous in a fully remote workplace? Some ideas: a #work-memes Slack channel for customized jokes about your job or company; a round of GarticPhone; a wear-silly-hats meeting; "accidentally" forgetting to remove your dragon onesie before joining a video call.