Fast walking with some hills is great. It also reduced my stress quite a bit as after 20 minutes I would stop contemplating/planning and just walk. Doesn't matter the weather and much easier to do

Please do. Exercising and eating healthy is crucial as hell in managing plateau's and burnouts like this.

Honestly it doesn't really matter what you'll do (be it cardio, body-weight exercises, or weight-lifting).

At first you just wanna be consistent on literally anything, as long as you show up doing your thing every day, eating healthily enough every day, and resting as much as you need, that'll put you into that better head-space.