Thank you, yes Cloth in R25 is a different "engine", hence my hint with 2023-1.
I guess you have tested 2023-1, and the main obstacle is the rendering.
Using Alembic, you could animate everything in 2023-1 and render in R25.
Save your file, select your flag, and go to
Object Manager> Object> Bake as Alembic.
When the file appears in the Object Manager, disable the original Cloth.
Then select the Alembic Flag, and in the
Attribute Manager> Speed and Offset.
All the best