I need to rotate at work due to early-stage burnout, and fortunately my manager has realized it too and got me assigned to a new, interesting problem that I get

I need to rotate at work due to early-stage burnout, and fortunately my manager has realized it too and got me assigned to a new, interesting problem that I get to lead. But my need to rotate stems from a big project I am 90% done with, and iteratively bug-bashing to get to 100% and launch it. I need to finish that project to become a Senior and really get started on the next problem. The alternative is switching jobs or teams, which I don’t want to do: my manager and coworkers are great, I am progressing my career quickly, and it would be impossible to get the same pay without sacrificing WLB. This creates an interesting dilemma: the harder I work in the short term, the more I risk burnout, but once I finish my current project I can take a long vacation and likely won’t feel burnt out once I switch tasks. If I try to take it easy so that I don’t accumulate burnout as quickly (or take a long vacation now rather than later), I simply accumulate burnout at a lower rate over a longer interval. I feel like a lot of people don’t burn out in isolation or completely unexpectedly, but because they are faced with similar situations as I am in. How closely can I flirt with it while still accomplishing career objectives?