Theoretically, the ESP-01 I've bought should have been configured as esp01_1m (Generic ESP8266 ESP-01 1M) on PlatformIO. However, it works flawlessly (and out-of-the-box) when configured as nodemcuv2 (ESP-12E).
I've kept both working configurations.
Oh – on Windows, install CP210X and CH340X drivers.1
And on Linux, remove brltty
and/or comment udev rules.1 2