If you are using a standing desk, please be either barefoot or in properly flat shoes. If in shoes, also make sure they are wide, thin and flexible.
We are not meant to constantly stand on a slope.
When people begin using a standing desk they often complain of lower back pain amongst other things.
My posture is not great but in this rudimentary example here, it can be clearly seen that my posture is better on the left, without a positive heel lift under my foot.
Starting from the feet, when standing on a positive heel (on the right) the forefoot is incorrectly over loaded, the ankle is in a plantarflexed position, the knee is loaded in a quadriceps dominant position, the pelvis is tilted anteriorly and the lumbar spine has increased curve. The negative changes continue to occur further up the spine, shoulder girdle and neck.
These things occur when wearing any sized heel and obviously not just at a standing desk.
As with any physical change, ease into getting used to being at your standing desk and being in flat shoes at your standing desk. Gently moving, adjusting your weight, single leg balances and calf raises / stretches can help too.