OpaqueFiles is a free and open-source project that can be used to encrypt data before uploading it to cloud providers or local storage.

Please also check out Cryptomator to see what suits you best.

Features
<ul><li>Encryption: ChaCha20-Poly1305 (default), AES-GCM-SIV</li><li>Remember password: Password can be saved in ~/.config/OpaqueFiles/opaqueFiles.properties to avoid typing</li><li>Compression: None, Zstd (default), gzip, XZ</li><li>Reed–Solomon Error Correction</li><li>Argon2id key derivation</li><li>Verification: Checks your encrypted files for errors during encryption</li><li>Checking: Check your encrypted files for malicious manipulation</li><li>Scrubbing: Check your encrypted files for corruption, and fix the corruption</li><li>UNIX Pipes</li><li>Stress testing: Test CPU/Memory stabilty. Faster but not as reliable as Memtest</li></ul>