You are correct about the leafminer symptoms, which is due to a native insect that does not cause serious damage to the plant and which can be ignored. The leaf spots are fairly common but we're not certain which pathogen is responsible. They too are very minor and do not need treatment. (What you already used is okay, but be aware that some fungicides might pose a risk to pollinators if applied around open flowers, or to other organisms if they encounter the residues. We don't have data specific to copper sprays, but in general, fungicides are not zero-risk.)

Fungicides can't cure existing disease, regardless of the pathogen responsible, though they can help to suppress infection on still-healthy growth. Most trees and shrubs are just about done producing the bulk of their new growth for the year by the end of spring or early summer, so few young leaves will be produced at this point, so there would be little to protect with additional sprays. Generally, protective sprays need to begin before symptoms manifest, earlier in spring, though at this point you probably don't need to worry about using more fungicide this year or next.

The reddish-brown blush to the leaf in the lower right of the collage image is probably just general heat stress, though not serious. The location for the tree will suffice for a few years, but be aware that Sweetbay Magnolia (unless a very dwarf and rare cultivar, which this isn't based on its current stature) will easily reach at least 20 feet high and about 10 feet wide or more when mature, and its trunk is located very close to the pavement for when its root system is more expansive and the trunk wider. It may grow suitably well in that snug location with limited root room and branch space for a time, but might not be able to reach its full potential, and as it ages, the roots filling that soil area may become more easily drought-stressed in summers with limited rainfall. You don't necessarily have to move it now, but this may be something to think about. (If you opt to transplant it, wait until next spring. Early autumn is an excellent time to plant and move most trees, but Magnolia reportedly is more sensitive to the root disturbance and responds better in spring.)

For now, just keep monitoring it for watering needs, and if a few older leaves yellow and shed, that's normal for many species of tree during summer. By checking the soil before watering, that will help avoid over-watering if you find the soil is damp several inches deep. Fortunately, Sweetbay Magnolia is more wet-tolerant than drought-tolerant, at least to a point.

Chlorosis is the type of nutrient deficiency symptom associated with soil pH that is too high for acid-loving plants. We don't see any chlorosis in the pictures, but if it appears, you can check the soil pH (and see if any other key nutrients are low) by submitting a soil sample to a testing lab, which will provide more accurate and detailed results than home test kits and soil probes. (We can help to interpret the results if desired.) Regular fertilization normally would not be needed for trees, but given that the limited root zone that is shared with other perennials here, a mild occasional dose (maybe once a year at most) is probably fine to use to supplement what might not be provided by letting leaf litter and other organic debris sit in place and self-compost.

Miri