This doesn't seem very agile. Without developer input into the sprint planning meeting this is going to lead to 3 hard weeks where overtime is highly likely because the team didn't have any say on what work was done and 1 week off to recover.

Whilst this may help with burnout so do the main implementations of agile when done correctly.

Agile done properly is all about quickly getting feedback on the speed of work so the business can correctly plan in accordance to this.