Popular in production = hard to get mostly. Eg you can get STM32G030 and similar at quite normal prices at LCSC (and thus JLCPCB assembly service, highly recommended over hand soldering BTW). OTOH stm32f030 (older and 2x worse in most respects) are way overpriced.
In addition to various esp32s (which have very decent sdk) you can easily get rp2040. You can also get a number of Chinese chips other than esp32 but good luck programming these.
I had success programming Chinese clones of the STM32F103C8T6 aka Blue Pill by just changing the device signature the programmer looks for via a flag in openocd. Fortunately these blue pill clones behave identically (so far, in my experience) to the real thing and are abundant and cheap on eBay so might be a good option for those who still want to work with a STM32 chip.
We're using ESP32s in everything, originally because they're pretty great (what's not to love about lots of IO combined with wifi and bluetooth?) but also now because they're the only thing you can get.
> What is actually possible to get your hands on now?
You can get your hands on many different chips right now, including many different STM32 microcontrollers. The more important question is "at what price" though, because some of these chips are more than 10x more expensive than years ago.
ESP32s in most (all?) variant are available. So are nRFs. Most ICs that were out of stock 1-2 years ago are avail again.
STM32s (most/all variants?) are unavailable. It's frustrating since these are very nice MCUs for a number of use cases. Ie fast, loads of hardware peripherals, variants and footprints to fit various project requirements.
In addition to various esp32s (which have very decent sdk) you can easily get rp2040. You can also get a number of Chinese chips other than esp32 but good luck programming these.