I saw questions with the same issue, but the given solutions didn't work in my case. After updating to Android Studio 3.5, all of the files and code appeared different (without coloring, for instance), and got the message
NDK Resolution Outcome: Project settings: Gradle model version=5.4.1, NDK version is UNKNOWN
I tried importing the project as instructed in another question post, and, as mentioned, it didn't work. Also tried "syncing the project with gradle files" and got the message:
ERROR: Missing Android platform(s) detected: 'android-29'
Install missing platform(s) and sync project
"Install missing platform(s) and sync project" is a clickable link. Clicked it and some update was made. Didn't help.
Any ideas?
EDIT
The solutions given in posts with similar questions did not solve this problem.