@MODERATORS: If this is far too much blatant advertising, please delete this post and apologies for any stress caused! Thanks.
While I’ve not been building any useful projects with PlatformIO, yet, I have written about it in my first (paper) book - Arduino Software Internals - whihc is currently on sale at 55% discount until 24th June, over at Apress.com. Use the “SUMMER55” discount code. (https://www.apress.com/gb/book/9781484257890#otherversion=9781484257906)
Chapter 6 of the book is devoted mostly to PlatformIO as an Arduino IDE replacement and covers the command line, and VSCode/VSCodium IDE versions, using the generated files with other IDEs (Code::Blocks etc) and so on.
Kind regards and thanks to all involved in creating this great platform for AVR (and STM32) development. I love it and I keep finding new stuff to learn.