If you increase the internal resolution, the quality will go up, 2x is 720p and 3x is 1080p for example, you don't need texture packs to improve quality. If for some reason this doesn't work, maybe you installed dolphin in a location that requires admin privileges and it can't make changes to it's config, you could try re-downloading a fresh version or making sure your documents folder for some odd reason doesn't require admin rights, you could also check your AV while you're at it.
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