This shows promise. Could use some rebalancing, but soothing core gameplay and great sound design.

Thoughts for the developer on the early access version:

• Immediately turned off by the aggressive marketing language; telling me how awesome the game is makes it feel like a cash grab, even though there's no monetization here at all. Words like "soothing" are fine because it's a good way to describe the game's vibe and tell me what makes this unique, but "satisfying"/"rewarding"/etc are things I should be deciding for myself or hearing from word of mouth. And I don't think you can describe levels as "hand-crafted" unless there's some gameplay variation such as new board shapes.
• I spent a long time clicking on the drop button before realizing that you could click-and-hold. I extremely appreciate the click-and-hold! I don't know if there's a way to make it clearer up front that that's an option.
• That said, manual drops scale insanely faster than passive drops. By midgame I was getting about 5 balls per second from click-holding as opposed to 0.3 balls per second passively. When I crashed the game in Space level by running it out of memory, I was up to 9 bps with click-hold and only about 0.5 balls per second passively. Different idle games have different opinions on how to phase out clicking/interaction in favor of passive income (see e.g. Crank, where you ultimately never touch the hand crank the early game centers around, vs Cookie Clicker, where clicking falls off but then later upgrades can turn active clicks into significant burst economy), but generally clicking shouldn't be the vast majority of your income throughout the entire experience.
• What I really liked: Watching the balls drop gets almost hypnotic, especially with the superb sound design. I reached the end of the content (space level) and ended up continuing to play until the out-of-memory error ~10 minutes later. There's a good niche for games that it's rewarding to have on in the background.
• Abandoning each level after you clear it feels like a waste of all the time you put into level design. I'd love to see some further reward for returning to earlier levels, or pushing them past the minimum required to proceed. Perhaps the score from each level provides a passive boost to some statistic that all levels use?
• Most of the text was unreadably tiny, at least playing it inside the itch window; it never bothered me since buyable elements lit up, but it might be worth double checking how elements visually scale.
• There are some levels, especially the early ones, where there's no visual difference between a basic peg and an upgraded (+1) peg, so I was initially confused what upgrading pegs did.
• Where's the neon in the neon level? I never got any lighting except for the pegs turning on as I upgraded them.
• Level lighting also seems to affect the progress bars on the slots, so you can't always see how the slot upgrades are going.
• There's a big random element of progression in peg upgrades, because if you luck out and the same peg repeatedly upgrades, going from +10 to +100 is a HUGE score multiplier, but the upgrades get too costly to make that happen about 2/3 of the time (I got gold pegs in two levels out of 7). I wonder if you might want to make it possible to buy a reset of all peg upgrades in order to let players "reroll" those random drops.
• Since slot upgrades already happen passively as balls drop, purchasing them always felt like a waste of money. Also, by the time you drop into a 3-point slot, in a reasonably upgraded board you'll have already hit 5-15 points of pegs on the way down anyway, so slots are already underwhelming. Maybe have the slot upgrade give a random slot a permanent x2 multiplier so that it continues to scale as the slot levels up?
• Coin effects were a little unbalanced. The disco ball is barely worth clicking on. The coin doubler was boring but functional, though it felt underwhelming due to short duration. I was never unhappy to see multiball (and it's fun to watch). Legendary balls is very nearly a game-breaker; I got into the habit of spamming manual balls before clicking on coins, just to see if I hit the jackpot by turning everything on screen into a x100. It's definitely okay to have some powerups be better than others, but it might be worth spicing up the less useful ones.

Anyway, thanks for your development work and hope this is useful!