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All I have to been able to find is the forum and some videos.
Here is the Quick Reference for SQLcl 17.2:
https://docs.oracle.com/database/sql-developer-17.2/SQCQR/toc.htm#SQCQR-GUID-0A65BC18-6AD2-4A6C-81CD-782D71BDBCB9
and although SQLcl may not support all SQL*Plus commands, or all options of those commands it does support, you can glean useful details from the SQL*Plus documentation:
https://docs.oracle.com/en/database/oracle/oracle-database/18/sqpug/index.html
Edit: Or better yet, for 18.4 -
https://docs.oracle.com/en/database/oracle/sql-developer/18.4/sqcqr/index.html