Hi, and welcome!
This is just a warning, not an error per-se. This appears because the instructions provided on Brave's website are designed to be the same regardless of whether people is using a 32-bit or a 64-bit computer. Because of this, both versions are checked for updates but only one of them is actually compatible with your computer. This is expected and harmless, so you can ignore it.
If you want to remove it, however, you can first run this command on a terminal window:
dpkg --print-architecture
And then update the file at /etc/apt/sources.list.d/brave-browser-release.list:
- deb [signed-by=/usr/share/keyrings/brave-browser-archive-keyring.gpg] https://brave-browser-apt-release.s3.brave.com/ stable main
+ deb [arch=amd64 signed-by=/usr/share/keyrings/brave-browser-archive-keyring.gpg] https://brave-browser-apt-release.s3.brave.com/ stable main
The arch= option specifies the architecture, which should match the result from the previous command. Here I'm assuming it will be amd64; change it accordingly.
I'm not sure about the other error. It looks like this is the result of some script that runs after an update operation, probably setup by something else that you've installed previously.