My preferred way is to have one symbol layer with all the symbols. It prevents having to constantly doing shift/unshift or switching layers (I personally call this "shift dancing") 😀

It looks like this:

https://keebogram.pages.dev/hypership/

I use a 30% split keyboard as my daily driver for work as a software developer. I use a keymapping where holding the F key down turns the right side into a numpad plus some of the other punctuation, and holding D down gives me the shifted versions of all that. So I have to chord to get the esoteric symbols but I don't have to actually move my left hand from home row to chord. I don't think this is a very common way of doing things though. I'm not sure it's any better than using a bigger keyboard, but I'm used to it now.

On my 34-40 key layouts I put all the symbols typically used together in programming on the same layer, including symbols that usually require Shift, along with all the numbers. This makes it comfortable to type whole formulas without leaving the symbol layer and without needing Shift. Important bigrams that I can type without switching layers in the middle include <= >= != += -= *= /= %= &= |= -> /* */ => := :) ;) . I also optimize the layer so that none of these are same-finger bigrams. Because = appears in so many bigrams, I found it convenient to map it on a thumb key.

I make sure all the mods are comfortable to use and in the same place on all my layers, either as bottom row mod-taps or on opposite side thumb keys or worst case as a oneshot mod. I don't need Shift on my symbol layer, so one less mod to worry about.

Probably my favourite feature for a programming key map is _ on a base layer thumb key. That makes typing snake_case_names a breeze.

Many people are forgetting the simplest answer here. Just use a full size keyboard. They are abundant and cheap. They come with ALL THE KEYS and don't make you layer shift in order to efficiently achieve what you need to do.

I ended up with pretty much my own entire layout. For the most part, I don't use layers, but instead use pairs of keys for symbols, numbers, etc. I also kept things largely where they are on a traditional keyboard, so that I'm not fighting against several decades of muscle memory.

The main issue with what I've done is that I'm kind of pushing past the limits of combining features with QMK. I use pairs of keys as modifiers (my left shift is 'E'+'D' for example), this key pressed is also '3'. If I roll on numbers, I end up with stuck modifiers. I've gotten fairly used to it, but it still hits me from time to time.

I do use a layer for things like cursor keys, though.

You should be able to cmd down > layer shift > symbol > layer release > cmd up. It sounds like a lot, but I don't need to do anything like that very often.

I'm a developer and I use a (slightly modified) miryoku layout for my daily driver. I know not everyone loves the home-row mods, but I really like how I can use the layer keys on one hand to get all the symbols on the other. I have to move my hands waaay less than I did with a full size.