Could you provide a little more information? What is the tree planted in, is it in-ground or potted, is it grown indoors or out, how often do you water, has it been fertilized recently and with what kind of fertilizer, any recent changes to the tree/environment? A lot of factors can cause browning of new growth and more information can help those with the knowledge to help you to do so.

Looks like scale. Can you provide a closer up pic? I'd treat at once if it is.

There seem to be signs of scale. Look under the leaves, along leaf petioles and green branches. The mature ones look like dark oval bump, and juvenile ones are more translucent. If you see something along those lines try to rub them off. If they come off then they are definitely scales. You can use a q-tip dipped in alcohol to "rub" them off. Use the q-tip to wipe along branches where see them and also along the veins in the leaves (usually underside but can be on the upper surface too).

I discovered scale from a store bought lemon purchased at a high end garden center. I was able to take a good pic of what they look like. I’ll post it. Biggest sign something was wrong besides the tree just not growing the beat was ants everywhere. The scales feed on plant then produce honey sucke which attracts the ants. It’s a dead give away.

The scale doesn't just attract the ants, the ants will actively farm the scale!

and what did you do to combat it?

Horticultural oil

more photos

I had the same and I was told by a horticulturist that it was mealy bug. Either scale or mealy, it needs treating. A botanist suggested that I set it outside for the natural predators to address it and it worked a charm. after trying to treat it for two months with horticultural spray, I washed it off and let nature take its course and within a few weeks, the outdoor bugs ate the mealy bugs. The weather is now cold where I live, so they are back indoors and I hope that it does not come back, as it did some serious damage to my Meyer lemons and kumquats.

Santiago: Your pictures did not post (your last post) or it is houzz behaving badly and not displaying the picture.