TCP is on a lower level than SSH, usually SSH uses TCP as its underlying transport layer. TCP as such is not encrypted, but it can of course be used to transport encrypted data.

Are those packages not part of the same SSH connection according to Wireshark?

I think SSH almost always uses a cipher by default. If you’re concerned about the security of it, or really do want to check the bytes are encrypted, then I wrote more about it in my long spoiler.

For your concerns, it sounds like the fear is that packets being sent may contain the exact bytes found in the files. This should be mostly easy to check, just sync a very small file with a set of bytes known, and if matching bytes are seen in the packets, it’s not encrypted. A goal of encryption is to have encrypted data appear as high entropy random data. As an example, a ceaser cipher does not look like random data and can easily be broken. In other words, if the cipher is good, the packets should look like they contain random bytes and not look related to the bytes in the file at all. The SSH protocol uses a set of ciphers, and it’s possible to specify which cipher should be used. In my opinion, I like cryptosystems that are being used on blockchains because they’re live proof that the cipher and implementation are secure enough to keep over a trillion dollars in value safe. Though, blockchains are commonly focussed on asymmetric key pairs that I think seem riskier when compared their symmetric counterparts. (Though, I don’t think there’s really evidence to support that they are riskier) I think SSH, and many protocols like https will commonly start with an asymmetric encryption method, then switch to a symmetric system. (for either security or performance reasons) There are technically methods to disable and not use encryption for SSH, but I don’t think these are included with clients, and are not defaults. Anyway, I think what you are trying to do, is take already encrypted files, and transfer them to a server for storage. SSH uses encryption in the transfer process, but that’s decrypted at the server side. If the server is being used for storage, then it sounds like you want the data to be encrypted for where it’s stored. This shouldn’t be difficult to verify, just check the files stored on the server are encrypted. (The bits and bytes of the files should not match the unencrypted version from the sending device.)