Cant update system

Dear Brave community,

Two questions…
1)
I use Linux mint (19 cinnamon)…cant seem to update my system…get the following message, so i think its an issue with brave.

GPG error: https://brave-browser-apt-release.s3.brave.com bionic InRelease: The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY A8580BDC82D3DC6CThe repository ‘https://brave-browser-apt-release.s3.brave.com bionic InRelease’ is not signed.Updating from such a repository can’t be done securely, and is therefore disabled by default.See apt-secure(8) manpage for repository creation and user configuration details.GPG error: http://dl.google.com/linux/chrome/deb stable InRelease: The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY 78BD65473CB3BD13The repository ‘http://dl.google.com/linux/chrome/deb stable InRelease’ is not signed.

  1. I used to be able to add Tutanota (email) as a web extension …for some reason i deleted it and now i cant seem to add it again…cant see it in the web store…any help appreciated (I have contacted them but no successful answer)

Thanks for any help