If it is full disk encryption or for file containers I plan to update regularly, VeraCrypt. It's quite capable and has quite a number of encryption options.
For individual file or folder encryption, 7zip. It's a very straightforward program that is worth having installed given how much good of an all-round zip program it is.
I've used VeraCrypt successfully to encrypt volumes/folders.
It's worked great for me, although I recently started encountering issues accessing files but it seems the problem is with my external and not with the encryption method. Hopefully I can recover those files someday. Backup your backups and then backup again.
My volumes are PLAIN dm-crypt encrypted (i.e. LUKS without the LUKS bells and whistles) and the key is stored on my Vivokey Flex implant.
I mount them using scripts that combine crypsetup and vivokey_pam, with the ubiquitous ACR122U RFID reader: the systemd service file calls my script, I present my implant to the reader and voila: the volume is mounted.
Honestly, yes. It's not fun when someone slices your skin open and then lifts your skin to create a pocket, even with lidocaine injections. But usually it's 10 teeth-gnashing minutes and then it's over.
That's for big planar implants of course. The smaller ones are glass tubes the size of a grain of rice and injected under the skin, exactly like chipping a pet. It's 10 seconds and then it's done. But those glass implants have reduced performances, especially for things like doing cryptography on the chip, which requires more power.
Is it uncomfortable to wear?
No. I've had mine for years and I honestly only remember they're there when I touch them.
Where do have it?
My Flex is in my right wrist. I have other implants (11 in total) in other locations. Mostly in my hands.
What other things is it useful for?
The Flex is used for cryptographic purposes (TOTP and computing hashes, the main purpose of the latter being those encrypted volumes). It's also used as a token to unlock my banking app on my phone.
All my implants are used for many things. I guess the best way to show them to you is to point you to this post I wrote a year and a half ago, in which I gathered all the videos I made to show their use in one post.
I use GPG if there's just like a single file I need to encrypt.
When I have to sync an entire folder to the cloud though, I use Cryptomator.
I have also used VeraCrypt before, as well as TrueCrypt back in the days.
Right now, GnuPG is absolutely safest for individual files. There's no age client for Android, and while I like it, I am allergic to encryption systems without a robust ecosystem.
Someone else just pointed out that DroidFS can read gocryptsfs directories, which greatly expands my confidence in gocryptsfs - which is my preferred short term directory solution. For archival purposes, though, tar+gpg is the only thing I trust to be available and working in a decade.
Tbh man, I use 7zip. I mean I know it's not all that secure from law enforcement or anything because with the quantum shit going on they're gonna break that in no time.