The following links represent useful resources for working with the IntelliJ Platform and creating plugins.
IntelliJ IDEA Conf 2021 includes a number of presentations related to plugin development
Busy plugin developers series. Episode 0 Mikhail Vink/Jakub Chrzanowski/Yann Cebron, 2020
How We Built Comma, the Raku IDE, on the IntelliJ Platform Jonathan Worthington, 2020
Building IntelliJ IDEA plugins in Scala Igal Tabachnik, 2020
Live Development of a PyCharm Plugin Joachim Ansorg, 2019
Build Developer Tools On Top of IntelliJ Platform Dmitry Jemerov, 2013