How to limit a job in gitlab ci to a tag matching a pattern?

Only accepts regex patterns so for your use case it would be:

only:
  - /^V.*$/
except:
  - branches
  - triggers

Since only / except are now being deprecated, you should now prefer the rules keyword

Things get pretty simple, here's the equivalent using rules:

rules:
  # Execute only when tagged starting with V followed by a digit
  - if: $CI_COMMIT_TAG =~ /^V\d.*/

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