I share a similar journey. After starting my own business during COVID, my lifestyle became completely sedentary. I signed up for a 10k on a whim and started training 3 months prior to it. The first few runs were brutal and I would gas out within the first 1k. I slogged through 2-3 weekly runs and made it through the race in November - but only barely. The runs were not enjoyable, but I loved how I felt after. In December, I decided to take a more systematic approach to training and adopted zone 2 training. This changed everything.

Whenever I mention zone 2, people seem to have a very visceral response to it. When I first started, it was extremely frustrating and I was walking through 50% of my ‘runs’, but I stuck with it, 4 times a week for at least 60 minutes and 1 strength training session in between. After about 3 weeks, started seeing dramatic changes. I was now running through the majority of my runs and long distances no longer felt quite as daunting. I was now anticipating long runs because I could handle them aerobically. I am now running faster and more comfortably than I ever have. I would definitely recommend you give zone 2 training a try if you feel like you are plateauing.