You reckon huge amounts of enthusiasm would be, somehow, tantamount to having a nice portfolio? Or would a portfolio carry much more weight? (take this question given the circumstances of a junior dev -- 1-2 years xp in back-end)

Sorry for the slow response, I just found the Threads index. :) If you have the nice work history, use it. If not, go with your strength. Most good employer devs were themselves doing Great Things when they were just out of the box and when reading resumes we are looking for that younger version of ourselves.