Say limited to less than 10ft of depth. Maybe three minutes of breathing - who cares. Just enjoy being underwater for a little bit and seeing things you can’t normally get to.
But way less expensive and dangerous.
"Oxygen rebreather" I was going to say, but the first image at https://www.divein.com/diving/rebreather/ set me back a ways. The diver looks like a giant version of a wolf spider.
The WWII oxygen re-breather was a smaller-than-SCUBA unit for shallow dives used primarily by special forces (it recycled your exhalations removing the CO2 and produced fewer bubbles at the surface to reveal your presence). It has been decades since I looked at this tech and at first glance it seems oxygen re-breathers have only grown bulkier.
So-called "mini-SCUBA" tanks are available priced in the low hundreds of USD:
https://duckduckgo.com/?q=a+smaller+scuba+setup&ia=web
Finally there's a DIY version based on the James Bond movie "Thunderball":
"Working 007 Mini Scuba Tank! - Breath Underwater With This Spy Gadget"
https://www.youtube.com/watch?v=LqLt_G2dhCI
A safer experience is an underwater drone:
https://bestreviews.com/electronics/drones/best-underwater-d...?
Most dive shops have "Discover Scuba" which is basically they give you some brief training, but then they go on a scuba dive with you to a shallow depth (6m I think?) and basically hold your hand the whole time.
My ex-girlfriend got into scuba that way. But they never would take you down to 6 meters the first time.
She thought that she mastered buoyancy control instantly.
Little wonder when you have a dive instructor holding and operating your inflator hose :)
It's a great way to figure out if scuba is for you.
People are constantly inventing new products to fill this niche. Snuba being one of the least objectionable ones. Most are just flat out dangerous and marketed to uncertified divers, you can see these on places like kickstarter.
Freediving is always an option, but fatality data indicates it’s more dangerous on average than scuba. Lack of training is a problem since anyone can buy a mask and fins and start doing it. Shallow water blackout is no joke.
It is better than Snuba.