Overlay modes were temporarily broken when a Freelancer tried to "fix" the "unwanted black flash", but that was backed out.  So as far as I know, they are working and if/when I catch up, I can test.  It was added 10/31/2021 and backed out 01/31/2022 when IgorBeg reported it.  Freelancer help is of little use as it takes real dedication and understanding to modify Cinelerra without breaking stuff.  Sad.