YouTube videos by Oracle https://www.youtube.com/@OracleAPEX
Blogs https://blogs.oracle.com/apex/
https://videohub.oracle.com/esearch/search?keyword=apex (some non-English content also)
APEX documentation https://docs.oracle.com/en/database/oracle/apex/index.html
APEX discussion forum https://forums.oracle.com/ords/apexds/domain/dev-community/category/apex
APEX community https://apex.oracle.com/pls/apex/f?p=411:18
Nasar's Blog 