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.
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.