This area should be step flashed. Also, it appears to have some nail pops and possibly an issue with slope at the transition.
In this photo, you can see a step flashing around the chimney. This appears to be functional and intact.
In this photo, you can see that the surrounding trees have branches that come into contact with the shingles. These should be trimmed back to prevent damage.
In this photo, you can see the presence of lichen and fungal growth. This is very common and it is known to damage shingles over time.
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