avi & mkv format are NOT supported by adobe premier

I don't know about Mac, but on Windows AVI is supported **IF** what is inside the wrapper is compatible

AVI is a wrapper, what is inside YOUR wrapper - Exactly what is INSIDE the video you are editing?
Report back with the codec details of your file, use the program below
Free program to get file information for PC/Mac http://mediaarea.net/en/MediaInfo/Download
- when you analyze your file in MediaInfo and post a screen shot in the forum, do so in TREE view
- post your information IN your message, not as an attachment that someone would have to download

NOTE - H.264 will not work inside an AVI wrapper https://community.adobe.com/t5/Premiere-Pro/Can-t-get-PPro-to-accept-video-file/td-p/3450861

Adobe has never officially supported MKV. That format was unofficially supported in CC 2018 12.1, until it was dropped starting with Premiere Pro 2019 13.1.3.