There are some surviving national circuits like PagoBancomat (as the sibling comment from Scrollone) and Dankort (Denmark) and girocard (Germany). My personal impression is that they are slowly going out of fashion in favor of visa/mastercard only (probably because they can’t offer better prices than them).
I don’t see a solution to the duopoly, apart from lobbying politicians to support this national payment infrastructure. Especially in recent times I can also see how some governments might not want to rely entirely on two US companies for running their entire economy, so something might move on that side, so there’s hope on that side.
The EU has already been moving on this front in the last years by forcing the banks to provide programming interfaces to initiate bank payments, and that’s why you can now see more and more options to “pay by bank” online in EU. These online payments generally skip card circuits and run over normal SEPA bank transfers.
More info here on the last part: https://en.m.wikipedia.org/wiki/Payment_Services_Directive
For fstab editing, try running “mount <path>” and check if it succeeds before rebooting, so you can still edit if there are mistakes. FYI if you do a sytax mistake in fstab the entire OS might fail to boot. If it happens don’t panic, it’s easy to fix: you can use the install usb drive to edit fstab on your disk and try again (no need to reinstall!)
There are also graphical tools. I never used them, but it might be easier if you are not feeling super sure on what to do: https://superuser.com/questions/346606/is-there-any-gui-tool-to-configure-etc-fstab
I also use steam to manage external launchers. It’s a bit clunky, but it keeps proton updated and works quite well once it’s set up.
Welcome to linux, and do ask around for help / tips if you need!