Hello @Kamila Chęcińska
Welcome to the Atlassian community.
How are you telling Jira the members of each team leader's team?
I think that the only way you will be able to do that is to add the Team Leader to another custom User Picker field, and then add that custom field as part of the the Security Level.
You could use Automation Rules to evaluate the Reporter field and then set the Team Leader field appropriately.
Thank you! It works!
Glad I could help.
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