I know keeping an active encrypted volume (like a VeraCrypt drive or a simple zip folder encrypted with AES256) on Dropbox/OneDrive/Gdrive/etc. is risky; data can be corrupted and the pattern of modifications can be a clue to an adversary, as is well explained in this thread. But what if it is never modified or shared, is it still risky?
If it is never modified, and is always at rest, then the confidentiality of the contents will be as strong as the encryption key. In other words, an attacker would need to know the encryption key (or the password it is derived from) in order to decrypt the contents. However, know that VeraCrypt uses XTS mode, which is not authenticated. An unauthenticated mode means that it may be possible for an attacker to make predictable modifications to the plaintext just by modifying the ciphertext, without even knowing the key. For XTS, an attacker can randomize any 16 byte sector. If integrity is not part of your threat model (for example, if you digitally sign the volume), then this is not an issue.
There's many different types of "risk".
Risk of accessability - The cloud service abruptly goes out of business. The drive(s) storing your data may crash.
Risk of confidentiality - Is the passphrase you're using strong, and not reused multiple places.
Risk of integrity - Are you signing the file, or just encrypting the archive?
Then there's always the small risk that there was a bug or error in the code which implemented the encryption algorithms, which could result in a vulnerability being found in the future.