Are you facing problem, when you try to change theme and Content -> Design – > Configuration page stuck in keeps loading? Nothing is happen and it’s freeze admin. Even some time you can’t move to dashboard from configuration page.

This can be resolve by any of b

1) Any third party extension try to load any static resource. So Make sure that everything loading proper by debug “Network” tab of browser and there is no error in browser console.
2) Remove files of /pub/static/ folder. Make sure you don’t remove .htaccess file. & Remove /var/ directory.

3) Execute below command:

php bin/magento cache:flush
php bin/magento setup:static-content:deploy -f
php bin/magento indexer:reindex (optional)
php bin/magento setup:di:compile (optional)

4) There is also possibility to disable “spinner” Html element using style display:none.

Hopefully any of solution work for you. Happy Development. Enjoy :-)