[2021] Game not allowing multiple saves between single and multiplayer - Games being overwritten when trying to switch between the two..

Local saves are kept here:
Documents/Paradox Interactive/CK3/save games/

Cloud saves are visible here:

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Do you see these missing saves in either place?  

It is hard to see how a save file with one name could overwrite a save file with a different name. Is that what you are saying?  

I have no idea what could possibly do that, I am sorry. Overwrite really means the same file name!