When I minted at development mode and checked the Solscan page, the "isOnCurve" part was marked as False.
Question mark says it means "An off-curve address is any address which cannot have a corresponding private key"
By any chance, even though minting has been working normally (the last minting was in January 2023), if I received a false value at "isOnCurve", can you tell me what the cause is?
"isOnCurve" denotes whether the given account is a PDA or not. As you mentioned, they do not have private key, but rather are PDAs are derived via seeds & a bump. Because of this, the program they were initialized from acts as the owner, and signs on behalf of the PDA.
My assumption from this screenshot is that you're looking at an "Associated Token Account" which indicates an account that holds tokens (token account) which is derived via the Associated Token Program. This means that it's totally normal that this account would show a "isOnCurve" of false.
For a bit more detailed answer and explanation on PDAs, read this answer
