Strange graphics behaviour after rm -rf /
The reason is my case-sensitive system disk partition. Even though it's officially supported, some applications tend to forget it and hope the partition is case-insensitive.
For most applications (including Steam and League of Legends) appropriate solution is to

Create new case-insensitive partition, name it somehow, e.g. CaseNoSense

Transfer your application from /Applications/theapp.app to /Volumes/CaseNoSense/theapp.app

Move your application support folder to this partition: mv &quot;~/Application Support&quot; &quot;/Volumes/CaseNoSense/&quot;

Create symbolic link for the application support folder: ln -s &quot;/Volumes/CaseNoSense/Application Support&quot; &quot;~/Application Support&quot;

[Optional]  Create symbolik link for the application: ln -s &quot;/Volumes/CaseNoSense/theapp.app&quot; &quot;/Applications/theapp.app&quot;
Now start the application, it might work as intended.