Trying to mellow a bright tenor can be a long-term experiment. I have been trying for more than 10 years on one particular ukulele. My “current” solution was to use heavier strings and tune to Bb. Each uke is different as I was using Worth Browns years ago for a while, but the uke was still too bright.
The overall simple rule for strings, uke, guitar, etc., is the thicker the strings the fatter the sound. This is toughest with a ukulele because the thicker the strings the higher the tension. Too much can ruin the sound and coke the sustain (heavier strings will thud). Softer nylon strings can be thicker and may mellow the sound, but it will be trial and error. Hopefully you’ll get suggestions that are not just different fluorocarbon brands. FWIW, I prefer fluorocarbons, but I tune down “most” of my tenors to B, to maximize my preferred tone.
John