For PCs and notebooks there is the open source program VeraCrypt, which runs under all common operating systems (Windows, Linux, MacOS). This software creates an encrypted file container, which is made available as a new drive and can be filled with data. As soon as the data no longer needs to be available in the work process, the container can be closed and the files are protected from any further access. VeraCrypt is not suitable for encrypting files for a cloud service, as it stores the data in a large container, which must then be uploaded to the cloud service in its entirety. For cloud services there are other programs that encrypt each file individually, e.g. Cryptomator or BoxCryptor.
Detailed information on the encrypted retrieval and sending of e-mails can be found on the e-mail security page.