Estimations
Easy Agile Programs allows for capacity management on the Team Planning Board for Scrum boards.

The team's capacity can be manually entered for each sprint, allowing for capacity changes due to holidays and other commitments.
Estimates can be added directly to each issue from the Team Planning Board. Simply click on the grey field in the bottom left hand corner to add the team’s estimate. The story points are added up and shown at the top of the sprint so you can easily see if you are over- or under-committed.
Troubleshooting estimation and capacity
Failed to update capacity due to permissions
Error message:
Failed to update capacity of [sprint name]
To update this sprint, you must either have the Manage Sprints or the Edit Sprints permission for all of the following projects: [project list].

Resolution: A Jira Administrator can grant “Manage Sprints” or “Edit Sprints” permission by editing the project’s Permission Scheme in Jira Cloud or Jira Data Center.
Why can’t I see/set sprint capacity on my Team Planning Board?
To see sprint capacity on the Team Planning Board, the Board setup needs to:
be a Scrum board (not Kanban or a team-managed project)
use Estimates in Story Points (not time estimates)
Why don’t you allow estimations for Kanban boards?
One of the challenges we have with estimation is that Jira itself doesn’t support estimation on Kanban boards. Technically you can add an estimation field to the screen and enter values but Jira won’t understand it as an estimation.
Kanban boards are missing the settings screen to configure estimation, any reports around estimation and most critically for us, the APIs to set / update the estimation.
We typically try to follow Atlassian's lead on features like this as it would be challenging to maintain our own implementation of estimation configuration.
Do you estimate sprints in other units? Do you use estimates on Kanban boards? Let us know here.