As per the upgrade instructions:
Make sure your apps are compatible with the new version, so they keep working after the upgrade. You'll need to disable all incompatible apps as they might affect the upgrade.
But I can't find Manage apps option by going to settings icon on Jira 7.6.
As I'm updating Jira from 7.6 to 8.4 is there any other ways to check Jira app compatibility.
Introducing Jira Cloud for Excel Here at the product integrations team at Atlassian, we are thrilled to announce the new Jira Cloud for Excel add-in! This add-in lets you export Jira data directly ...
Connect with like-minded Atlassian users at free events near you!Find an event
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no Community Events near you at the moment.Host an event
You're one step closer to meeting fellow Atlassian users at your local event. Learn more about Community Events