First check ports. I think your hosting/server is blocking port 25, 465, or 587.
Check this url : https://github.com/mageplaza/magento-2-smtp/issues/97
Second : Flush your storage and caches. Run these commands :
php bin/magento c:f php bin/magento setup:upgrade php -dmemory=1G bin/magento setup:static-content:deploy -f
My problem solved with these steps in past.