Linux Mint 21 will finally end the Linux Mint 20 series, which is based on the Ubuntu 20.04 LTS (Focal Fossa) operating system series, featuring a newer base from the upcoming Ubuntu 22.04 LTS (Jammy Jellifish) long-term supported operating system series.
Of course, Linux Mint 20 will still be supported until April 2025 with software and security updates, but the Linux Mint team is now focusing on the next major series, Linux Mint 21, which will ship not only with newer core components (e.g. Linux kernel, Mesa graphics stack, GCC, GNU C Library) but also with a newer version of the in-house developed Cinnamon desktop environment.