File Encryption Tool
File encryption protects individual files or file systems by encrypting them with a specific key, making them accessible only to the keyholder. Unauthorized users will still be able to copy encrypted files, but they will not be able to open or view them without the password or key.
Windows: 7-Zip
7-Zip is a free and open-source file archiver. 7-Zip supports AES-256 encryption to keep your data safe. That's one of the most sophisticated and widely used security protocols by giant companies to date, which includes the CIA of the U.S. The 7-Zip is one of the best archiving and compression tools in its field.
To download 7-Zip: https://www.7-zip.org/download.html
How to encrypt files using 7-Zip: https://www.uvic.ca/systems/support/informationsecurity/fileencryption/encryptfile7zip.php
macOS: Keka
Keka is a free file archiver for macOS. Just like 7-Zip for Windows, Keka supports AES-256 encryption to keep your data safe.
To download Keka: https://www.keka.io/en/
How to encrypt files using Keka: https://ccbcmdkb.blackbelthelp.com/it/how-do-i-use-keka-to-encrypt-password-protect-files-and-folders-mac/
Android: Cryptomator
Cryptomator encrypts your files before they reach the cloud storage solution you are using and you may download it on Google Play for $5.99. Local encryption means your data is safe should someone gain access to your cloud storage account.
iOS: Cryptomator 2
Cryptomator 2 encrypts your files before they reach the cloud storage solution you are using just like Cryptomator on android. Cryptomator 2 is free (offers in-app purchases) on iOS. Local encryption means your data is safe should someone gain access to your cloud storage account.