Yes, it is fully offline, you can back it up by any mean you could any other file, and it should be fine as the files are encrypted (should store the keys separated), can be a USB, an external drive, another computer in your LAN, a git repo, nextcloud, syncthing.
How do I back it up to USB drive?
You copy and paste the files
What does the day-to-day operation of Pass compared to Keepass look like?
As I said I use qtpass as a GUI so, open qtpass, search for the specific password file, double click, put the password for my gpg key and then the password I need is stored in clipboard for 30sec (this is customizable or can be disabled) and I paste it where I need it.
If I need to store a new password, just use the add password button, and input the data, it is that simple.
What does the day-to-day operation of Pass compared to Keepass look like?
Someone else can confirm but Keepass seems to use symmetric encryption, whereas Pass definitely uses an asymmetric key pair.
This is why I gave up on Pass. Obviously it has its advantages or they wouldn't have done it, but personally I find that this is too much complexity for something as critical as password storage. I want to be able to access the vault with a single memorized master password and nothing else. That is only possible with symmetric encryption.
I'm guessing, they did it this way, because there's no persistent process to keep the decrypted files open. You'd need to ask the user for the password for every single command they run. With GPG, that persistent process is gpg-agent.
Of course, encryption with a GPG key is also going to be more secure than the longest password you can come up with.
I guess, many people will want access to GPG, too, if they want access to their passwords, so they're not bothered by it.
But yeah, I do also remember setting that up on Android, where you need a separate app to do the GPG, and it really stops feeling simple pretty quickly...
I second that. The official documentation is always the place to start.
Then, if you need more info or other explanation I usually recommend looking at the arch wiki. Whether or not you're using arch, instructions there are valid and one of the best you can find.
You create keys to encrypt your data, and keep the encrypted data in git locally which can be cloned to github, gitlab and the like.
It's just files on your computer, so you can back them up that way, or use a thumb drive as a remote git repo and push to it.
Day to day
Type pass and tab complete to find the entry. Enter the command and be prompted to unlock it. It will then print the credentials to the terminal.
To create a new password, you type and add command followed by a name and a text editor opens up for you to type credentials in, or it can generate them for you.
To keep your backup up to date you just git push to the remote of your choice. I use github
The initial setup is a bit complicated but once done and integrated with rofi or dmenu it's a really nice simple and secure way to do passwords. I remember following some Luke Smith video to get setup with it. You don't need to use git as someone in comments has said - (I don't) that's just a possible back up solution. Nowadays I just super p and type for the service I want and it copies the password to the clipboard.
It's a password manager that's conceptually kept as simple as possible. It's essentially just a bunch of GPG-encrypted files in a folder structure. But you can then get various GUIs and apps to interact with it, if you prefer.