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Focus on soil and water management. Trees with nutritional deficiencies and water deficit or excess will be more vulnerable to pest and disease issues.
The best is a soil test and prescription mineral and biological amendments. But a general purpose, natural/organic, slow release fertilizer is next best.
If you use 70% Neem Oil (clarified hydrophobic extract of neem oil), its a fungicide, miticide and insect pest repellent. But a one time application will not be effective for more than two weeks or so. You need to repeat the application every two weeks during the growing season.

This could be due to dry weather or too much rain, pests, diseases and lack of fertilizer.

https://www.gardeningknowhow.com/edible/fruits/mango/growing-mango-trees.htm

There is nothing wrong with it, other than needing a little water. They will naturally do this in response to heat, or dry weather to preserve moisture and cut respiration rate.

This article will give you more information on the care of these in container: https://www.gardeningknowhow.com/edible/fruits/mango/mango-trees-in-pots.htm

It is somewhat normal for the leaves to hang, especially the new growth. From the photo it does not appear unusually wilty. But you should consider stepping up the watering, flood the pot to the brim a couple of times in order to get good saturation and depth of infiltration. Consider using a soil moisture meter to take the guess work out of watering.
https://www.domyown.com/luster-leaf-rapitest-mini-moisture-tester-1810-p-7732.html

Something like this:
https://www.domyown.com/dr-earth-home-grown-organic-potting-soil-p-9497.html

The heat is not a problem for tropical mango, but the temps in Tracy can get down to below freezing, 25 degrees or 20 in the coldest spots. This will freeze your mango. So like citrus, you will need to protect it from frost, or choose a tree that is more compatible with your climate.

I suspect water deficit and/or nutrient deficiency.

Soil fertility and water management are vital for plant health, flowering and fruit development.

Irrigate during the dry season. Water a wide area not just near the tree trunk, water the entire area of the absorbing root zone which spreads as far as the foliar canopy and more.

Water deeply to wet the soil a minimum of six inches (15 cm), preferably to 10 - 12 inches (25-30 cm). Check this the next day, by digging down in a couple of spots to see how far the water infiltrated.

Fertilize at the beginning of rainy season, or according to local agricultural advise, with a complete organic fertilizer, composted/aged cow or chicken manure, or a chemical fertilizer like 15-15-15.
Mulch the soil surface to help retain soil moisture during the dry season.