Arduino, PlatformIO and Adafruit. Arduino is three things: an IDE, an actual development board and a hardware abstraction library. You only want the last one.

Arduino, PlatformIO and Adafruit. Arduino is three things: an IDE, an actual development board and a hardware abstraction library. You only want the last one. PlatformIO is a tool like npm or cargo - it manages dependencies and tool chains for you. It also has an IDE in the form of a VScode plugin, that is pretty nice, but you can also the CLI tools only (which I do). Adafruit is a great company making development kits - PCBs with microcontrollers you can program. They also make a lot of breakout boards - i.e. sensor on PCBs that are easy to connect to the development kit. They also write libraries AND they write great tutorials. If you like Python, there is also MicroPython - it isn't fast, but it is easy to use, you probably already know Python, and you still learn about embedded topics like GPIO, I2C, SPI and so on. If you are into Rust, there is a strong working group for embedded in the Rust community and they also have some nice docs. Not so much entry level, tough.