There are different “levels” that should be chosen for each software.

• try to use Flatpak for most apps. Check flathub.org and try to find officially supported apps (☑️)
• flatpaks can’t do everything though. Some apps need broad permissions, for example Browsers, VPN apps, many Terminal tools. These should be installed as native (.deb, .rpm) packages from repositories Examples: Waydroid, tlp, flatpak, distrobox, podman, virt-manager+qemu+qemu-kvm
• sometimes those packages are very out of date. Especially on Debian and other “stable” distros, just avoid these for Desktop usage. In those cases compiling can help, but it will be hard to remove again, or update or anything. Honestly I have no idea how to do that really.
• so if shit breaks, try Distrobox and install native packages for Fedora, Arch, Opensuse, as those may just work.
• Nix can also help. On Ubuntu you should just be able to install that. A really modern and community focused beginner Distro family, UBlue has “fleek” which allows to install Nix anywhere, easily.

As you are on Ubuntu, you may want unSnap. Ubuntu simply is not the “easy beginner Distro” anymore. It is very opinionated and does things like Snap that no other Distro is doing.

If you are a beginner and want a Distro that just works, I highly recommend Fedora Silverblue from ublue.it. installing packages is not hard, and normally only done via Flatpak. The rest is like on other Distros, avoid installing random Appimages or .deb/.rpm files, as they are not verified.

No this is the best way.

Apps on Linux have different “layers”. If you want an app like MullvadVPN, fast updates, integrated to your system, controlling DNS, blocking early boot connections to be completely air-tight, you need to do this.

The easy way would be sudo dnf install mullvad-vpn on Fedora. But its not in their repositories, so all you do is add the repository and install it.

The same with Browsers, I recommend Brave and Librewolf, install them from their repositories and NOT from Flatpak.

All the other apps from Flatpak, use the Flathub repository.

Once set it up, then it works.

Not at my computer, but you might check if there is a snap or flatpak

Some apps can only be installed from their own repositories. That usually involves some faffing with aging let’s to your key store, etc. That’s what the cryptic instructions are about. Most apps can be installed with one click from the distro’s main app store. Ubuntu is somewhat restrictive here, because it forces you to use snaps, which is their own proprietary packaging format. Other distros, e.g. Mint are more inclusive here. This is why Ubuntu isn’t recommended as much any more.

While lvxferre’s instructions are the ideal, there’s a simpler option

Download the mullvad.deb file.

Doubleclick on it from your file manager and it should automatically instsll

Every time you start mullvad it will check if the version is current and prompt you (with a link to click on) to upgrade if it’s not.

Note that works on mint, should work on ubuntu unless they’ve disabled dpkg