You can try Following ways
php bin/magento setup:upgrade
php bin/magento setup:di:compile
php bin/magento setup:static-content:deploy -f
Now, Login into admin panel & go to
Content => Configuration(Under design section) => Select your theme as Global.
Now again run following command in Cli
php bin/magento setup:upgrade
php bin/magento setup:di:compile
php bin/magento setup:static-content:deploy -f
php bin/magento cache:flush
chmod 777 -R var/ pub/static/ generated/
You can check "theme" table in db & also check parent id of your theme.