As a lot of other people, when I decided to check out the STM32, the first development board I ordered was a so-called Blue Pill board (so named because most of them are indeed using a PCB with a blue solder mask. These boards are readily available and they can be extremely cheap at around $1.50 (on AliExpress).
These Blue Pill boards generally follow the same recipe:
- (Claim to be) Based on a STM32F103 processor
- Same footprint (I/O pins)
- 8 MHz main crystal
- 32.768 kHz RTC crystal
- USB Micro-B connector
- Programming header
Unfortunately, these boards often retail well below the cost of an actual STM32F103 processor (they are starting around $2), so most (if not all) of them are using various STM32F103 clones. ST themselves did not design the core in these processors. That was designed by and licensed from ARM. Other vendors can - and do - license the same core and build a processor which might not be exactly identical but almost and some of these are quite a lot cheaper than the original ST version.
A few of these board clearly use one of the clone processors and that is quite OK. Unfortunately, as is clear above, some also use clones which are LABELLED as something they are not.
In short - avoid these cheap clones as you would the plague and get something else - for example a Black Pill. They are not worth your time guessing.