All About Flashbacks
From Dr. Format:
Two articles on Flashbacks.
Basic Flashback Formatting
https://www.keepwriting.com/tsc/flashback.htm
5 Unusual Flashback Situations
https://scriptmag.com/screenplays/ask-dr-format-formatting-5-common-flashback-situations?oly_enc_id=0684G9277956A7U