Is it possible to leave Bangkok airport during a 10-hour layover?

See if you can change the flights so you have longer time, if less than 24h it still counts as "transfer" and not stopover. I've done this before. The airline did the change for free. If you're lucky

The airport is very far from the city and with Bangkok traffic it would be very risky to do via taxi. You can take the airport link and connect to the sky train but unless you know what your doing it will be time consuming. The airport isn't too busy these days do when you get back you could clear security and immigration quickly but you don't know if there is a big tour group ahead of you.

I would not even try it personally.

Provided you had all the documents in order, it would take an hour from the time you land until you are outside the airport. BKK Airport has a train that can take you to the heart of the city, its about 1 hour ride. You're looking at minimum 4 hours to/from maybe more. That gives about 6 or fewer hours to mess around in BKK. To play it safe you would want to keep it to about 4 hours of messing around downtown.

I guess its worth it, but it's kinda of a pain in the ass. If I had never been here and had no plans on returning, I would do it.

Nope

Depending on where you are coming from and going to, you're probably much better off transiting somewhere else. Even people coming from Phnom Penh/Vientiane/Yangon are now transiting in Singapore or Seoul rather than putting up with the shambles that is Bangkok. Pre-Covid, most of these folks would transit in BKK but not anymore, since the Thai government decided to kill tourism and airline transit traffic.

I would just change my itinerary and stay in Bangkok for a month.

I think risky

You mention you are transiting between international flights, will you go through Customs and Immigration in Bangkok? If so, you can leave the airport, but as mentioned by others, you will then need a Thailand Pass, Insurance and Vaccination records and also as mentioned, time is your enemy.

It's probably easier for you to transit in Singapore.

I couldn’t comment on whether it’s allowed. I suspect not but I’ll let others confirm.

Even if it were I doubt you get much done. 10 hours seems a long time but the city is anywhere from 40 minutes to 2 hours away depending on time of day and traffic. You’d want to be back at the airport 2 hours prior to do immigration and security. Say traffic is bad. 1 hour to clear immigration, 2 hours in, 2 hours back - 2 hours prior would mean you probably only have an hour or so in the city. Not worth the hassle.

Relax in the airport, have a meal and drink or two. Read a book.

You will need to apply for a Thai Pass, have insurance, your vaccination cert, collect your bags and clear customs. Then checkin again 3 hours before your flight.

Yes, but you'll need a Thai Pass and travel insurance, plus meet the vax requirements