By default, Institution Admins can view any Space in their institution and will automatically be granted host permissions if they join that Space. Site Admins will have the equivalent permissions for all Spaces associated with their sites.
This behaviour can be turned off if your organization prefers tighter controls where admins can only access Spaces that they have been explicitly invited to.
To adjust this setting, you can follow the steps below:
Click on the 3-dot icon on the top left corner and click 'Settings'
Go to 'Permissions' from the Settings menu and toggle the 'Grant admins access to all the Spaces'. Click on Update to save the setting.