If you’re just starting with Ubuntu, maybe change before you have a lot invested in it, @jubilee, but Ubuntu is fine. Note that Mint is based on Ubuntu, so in many ways they are very similar. I used Ubuntu off and on from version 4 to version 16 and beyond, with a laptop using it full time from version 9 to version 11. I’ve also had Mint installs going off and on since version 17 or so, native and virtual. Other distros, too. I tinker.
I set up a virtual machine using Ubuntu 19.1. It looks like Ubuntu’s handling things a little different from Mint is all; the settings we want in this case are in Software & Update instead of Software Sources. There are two things to check: repository entry and authentication of the repository.
If you do decide to switch to Mint, please post that and ignore the rest of this post. The process of creating the rest of this post was fun and instructional and will be useful (to me if no one else - tinkerer) even if you switch.
First, open Software & Update, click on Other Software, and look for the first Brave entry (not the one followed by “(Source Code)”. If the entry has only http and not https in it, click Edit and add the s.
Click Authentication and see if there’s a key listed for Brave. If there is, you’re probably good to go. If not, then you need to open a tab in Brave or another browser and click/use this link and save it to Downloads folder: https://brave-browser-apt-beta.s3.brave.com/brave-core-nightly.asc
Now return to Software & Update -> Authentication, click Import Key File, navigate to Downloads, and import find the file you just saved there. Click Close and let Software & Update refresh the cache if prompted (you should be prompted). If you don’t get any error messages, you should be able to update Brave using Software Updater.
It should go something like this. The movies are at 50% scale; clicking one will enlarge it. I apologize for some missteps and extra stuff they show, but I’m tired and don’t want to take the time to redo them.
This is the first part checking the repository entry and presence of the key:
This is the second part downloading and, even though the key’s there, demonstrating by adding the key plus refreshing the cache:
Opening Software Updater to let it check stuff. Since I just installed Brave, I didn’t expect it to tell me it needed updating, but if there’s an update today that would change.