Hi Garama -
As of yet there isn't an official native Jira feature that tracks a user's time off - however there is a feature in development which is meant to tackle this case natively called Individual Capacity Planning here if you'd like some more information about it. https://community.atlassian.com/forums/Jira-articles/Introducing-Individual-Capacity-Planning-in-Jira-Join-our-Early/ba-p/3161425