Upgrades to Linux Mint 21 from Linux Mint 20.3 are now open. Users can use a graphical tool to perform the upgrade, making the experience a bit easier. Be sure to make a backup first.
Upgrade tool RSS
The Linux Mint team has released a stable version of the Upgrade Tool so LMDE 4 users can now upgrade to LMDE 5. Unfortunately, you still need the terminal to install the Upgrade Tool.
The Linux Mint team is finally working on an upgrade tool that will give users a graphical way to upgrade to new major versions of Linux Mint. It will be available in a couple of months.