Sadly, it's not simple. The user configuration folders are not well-documented and have historically included a bunch of default junk, which is slowly being stripped out (see https://youtrack.jetbrains.com/issue/IDEA-128660 and https://youtrack.jetbrains.com/issue/IDEA-163616). The documentation of settings files is also very poor; my request for improvement was declined https://youtrack.jetbrains.com/issue/IDEA-154157).
I version control my settings. If you request access, you can see it at https://gitlab.com/jcrben-staples/dotfiles-group/dotfiles/tree/master/config/intellij-idea-latest with notes at https://gitlab.com/jcrben-staples/dotfiles-group/dotfiles/tree/master/config/intellij-idea-latest/MY_CONFIG_DOCS.md).
I set up my .gitignore
to ignore everything by default, and then I whitelist the files that I want. With IntelliJ, I didn't know where to start, so I whitelisted the entire folder and then blacklisted a bunch of the files.
My blacklist doesn't exactly answer your question about what files to include, but it does give you an idea of what to exclude. I'll try to update this if I figure out which ones to include at some point, but it's a mishmash of plugin files and such.
Right now the blacklist looks something like this:
# IntelliJ IDEA stuff
.idea
!config/intellij-idea-latest/**
!projects/bi-idea/workspace.xml
# statistics files
config/intellij-idea-latest/options/statistics*
config/intellij-idea-latest/options/feature.usage.statistics.xml
config/intellij-idea-latest/options/usage.statistics.xml
config/intellij-idea-latest/options/statistics.application.usages.xml
# user files ??
config/intellij-idea-latest/user*
# other
config/intellij-idea-latest/options/atlassian-ide-plugin.app.xml
config/intellij-idea-latest/options/cachedDictionary.xml
config/intellij-idea-latest/options/customization.xml
# has my autobracket disable
config/intellij-idea-latest/options/CodeGlance.xml
# config/intellij-idea/options/editor.codeinsight.xml
config/intellij-idea-latest/options/databaseDrivers.xml
config/intellij-idea-latest/options/debugger.xml
config/intellij-idea-latest/options/dimensions.xml
config/intellij-idea-latest/options/extensionsRootType.xml
config/intellij-idea-latest/options/filetypes.xml
config/intellij-idea-latest/options/find.xml
config/intellij-idea-latest/options/find.recents.xml
config/intellij-idea-latest/options/jdk.table.xml
config/intellij-idea-latest/options/gemmanager.xml
config/intellij-idea-latest/options/github_settings.xml
config/intellij-idea-latest/options/gradle.run.settings.xml
config/intellij-idea-latest/options/extensionsRootType.xml
config/intellij-idea-latest/options/hg.xml
config/intellij-idea-latest/options/ignore.xml
config/intellij-idea-latest/options/markdown.xml
config/intellij-idea-latest/options/multimarkdown.local.xml
config/intellij-idea-latest/options/multimarkdown.shared.xml
config/intellij-idea-latest/options/options.xml
config/intellij-idea-latest/options/other.xml
config/intellij-idea-latest/options/packages.xml
config/intellij-idea-latest/options/pomodoro.state.xml
config/intellij-idea-latest/options/project.default.xml
config/intellij-idea-latest/options/proxy.settings.pwd
config/intellij-idea-latest/options/recentProjects.xml
config/intellij-idea-latest/options/recentProjectDirectories.xml
config/intellij-idea-latest/options/remote-servers.xml
config/intellij-idea-latest/options/runner.layout.xml
config/intellij-idea-latest/options/scratches.xml
config/intellij-idea-latest/options/stubIndex.xml
config/intellij-idea-latest/options/updates.xml
config/intellij-idea-latest/options/usageView.xml
config/intellij-idea-latest/options/vcs.xml
config/intellij-idea-latest/options/window.manager.xml
config/intellij-idea-latest/options/window.state.xml
# turn off those auto-update messages...
config/intellij-idea-latest/port
config/intellij-idea-latest/plugins/*
config/intellij-idea-latest/tasks/*
config/intellij-idea-latest/extensions/
config/intellij-idea-latest/jdbc-drivers/*
# region START UNIGNORE IntelliJ
!config/intellij-idea-latest/scratches/
!config/intellij-idea-latest/consoles/
config/intellij-idea-latest/consoles/.history/*
# General settings
# config/intellij-idea-latest/sonarlint/
config/intellij-idea-latest/javascript/nodejs/**
# config/intellij-idea-latest/options/editor.codeinsight.xml # has my autobracket disable
# endregion END UNIGNORE Intellij
This leaves fair number of files which are not blacklisted - plus I symlink my .idea
files sometimes and version control those settings, although workspace.xml
has a lot of stuff and it changes all the time (see https://youtrack.jetbrains.com/issue/IDEA-163348).
Also, keep your eye out for "Share" buttons like the one shown for a scope below, as these seem to control whether the setting is shared to a configuration.

The most elegant set up for settings configuration comes from VSCode - hopefully at some point Jetbrains will figure this out and copy them:
