The last 5.X release definitely needs to be an LTS. That's unmovable. We can't have two active LTSs, it'd be a backporting nightmare and at best it would be a lie to claim we're actively supporting both.
An LTS now effectively means we can't start Plasma 6 for another year. I personally think that's too late we're at a point where some people are building certain plasma repos against Qt6 already. I can envision Plasma 5.25 being the last before branching. David