I have had APFS + encryption fail me once, where I wound up losing all data on the drive completely. It was just a copy of data so it wasn't a major loss, but it was something that concerned me.
As others have said, the simplest way is to just use APFS + encryption, copy the files, call it done.
However, what I do is format the external drive with ExFAT, and use Borg Backup with encryption. This ensures that I can pull the data off the drive, regardless of the data being on a Mac, Windows (with WSL2), or Linux. Borg Backup is an open source utility, and has a lot of presence, so it won't be going away anytime soon. The nice thing about Borg Backup is its deduplication, so if you back up a folder twice, the space used will be minimal.
Another idea is to use Cryptomator. This works on Linux, Mac, and Windows, and you create a vault (which is a folder with encrypted contents), mount that, and from there, copy your files into that. The nice thing about this method is that it works on all platforms (assuming you used ExFAT for the filesystem), and provides solid security.
If just Mac-only, the simplest will be using encryption with APFS, but making sure you have multiple copies on multiple drives, just in case.