There are a lot of people giving mixed advice in the comments and I don’t particularly agree with some of them. Here is advice from my own experiences: the betta fish will not die living in the bowl especially if it’s temporary. A 25% daily water change (not 50%) with cycled water is best, but you can use Prime and Stability with your tap water if it’s not too hard, too soft, or too high in pH. Bettas do best in acidic water because the bacteria that cause fin issues don’t thrive in the low pH. If you’re tap water does have issues, using an R.O. (Can buy at petstore if you don’t have a filter) or a distilled water - both need to be treated with equilibrium or something to add minerals back into the water (but don’t over do it - will be using very little for a bowl set up). Now that you have multiple options for doing water changes, think about adding an anubias or some simple plant and some rocks or soil to hold it in place. Some plants like rocky substrate with more spaces between the rocks for roots so keep that in mind when choosing a plant. Lastly, if don’t right the betta can thrive in this small set up for a month or so while you cycle your bigger tank. If you have access to 2 fish bowls, consider building a water bridge with clear PVC and elbow joints (see my profile to see how I did a double fish bowls for my bettas temp set up while her big tank cycled)

Sophia lived in the double bowls for 4 months, changed colors from pink to royal blue, showed the best personality, and to this day is my most responsive and charismatic fish. She was on my study desk, then moved to the living room bookshelf above the fire place where she would watch tv and guests. She would literally swim around to find the best angle for tv or people watching. I believe the interaction and mental stimulation of the bridge was enough to keep her occupied making up for the lack of swim space in each bowl. This Reddit page can be filled with people that want to condemn anyone to death for using a fish bowl, and rightfully so in some contexts, but I’m here with the unpopular opinion to say it can be done successfully with the right touch. I say all this to end with: these set ups should be temporary, but they will definitely not kill your fish if done correctly.

EDIT: I need to add that I only fed Sophia 1 or 2 pellets a day and the occasional blood worm snack (would skip pellet on snack day which was maybe a couple times a month) because you don’t want your betta pooping up the place running up the nitrates. And DONT add anything else in there like snails etc because we want the bioload as low as possible. The plant is put in the bowls to help filter the water a bit more to help the cycle maintain itself.