Navigate to Devices > Chrome > Apps & extensions > Users and browsers.
Select the Top level Organizational Unit or where the users are.
At the upper right part of the page, you'll see and click Additional Settings with a Gear Icon.
At the very first setting Allow/block mode, click Edit and change the option to Allow all apps, admin manages allowlist.
Save the changes and try deploying extensions again on your end.
Note: To propagate the changes faster, on the Google Chrome browser from one of the affected user's devices, search chrome://policy. Click Reload policies at the upper left part of the page and try again. Hence, you can also try signing out and signing back in to reload the policies and refresh it.
