If someone in 2021 is asking you to transfer secret information in an SD card, run. They are either a scammer or a cop. The only reason to do something like this is to get physical evidence, photographs documenting you handing over the information. Physical dead drops of encrypted information isn't a thing anymore. Real spies use dropbox, tor, rapidshare, or a thousand other ways to securely move digital files without physically meeting.
Encrypt it into a truecrypt container. AES-blowfish plus whatever other layers you think you need. Toss in some random junk to pad the size. Then rar-encrypt it again, splitting it into a couple 200mb volumes. Label it as some sort of porn and upload it to a filesharing service via Tor. If this is real spy stuff information then the recipient won't care about jumping through a few hoops to download the material. If it is the police then they will balk at the effort because it will be complicated to explain these steps court. The police will insist on an SD card in a sandwich.