More than 3 years ago we had taken a step back from our Plasma LTS Edition. It never quite fit into way KDE neon works as a product, nor as a project. Plasma was caught in the past while the rest of the system kept rapidly leaping forward, resulting in a less than stellar user experience and a huge cost in maintenance. All the while it has always been the least used edition.
We have consequently decided to draw the only natural conclusion and end support for the KDE neon Plasma LTS edition on 2021-07-01.
For users that absolutely want to use Plasma LTS, we recommend that you instead look at one of the actual LTS distributions such as Kubuntu LTS or openSUSE Leap that try to maintain a stable system as a whole, not just the desktop.
If you would rather stick with neon, which we would of course prefer 💕, you’ll have to switch to the regular KDE neon User Edition. We have created a handy guide for this, available in the KDE UserBase Wiki.