Is it first/last click?
What is the standard duration until expiry?
Where can I see this information for a specific UTM-link I created and how can these settings be modified (both for existing as well as new UTM-links)?
GA collect "hits", these hits represent data/values at a specific instant in time (userid/source/medium/content/browser/etc..)
GA only report on the data. If you want to look at attribution, you're able to adjust it yourself. It is flexible.
Instructions on how to change session timeout and campaign expiry. The default for sessions is 30mins and campaign expires after 6 months.
Here is documentation on how UTM parameters match up to GA data. You can usually find these under the Acquisition section of reports in GA.