XML-RPC.php file is a script file; added to WordPress to embed remote connectivity facility. This file enables remote connectivity between your WordPress and external app. I know, you didn't understand it clearly, so I keep it simple.
After installing centos8 as your VPS distribution, you need to change the root password as well as the user’s account password. Changing this credential is super easy in centos 8 VPS and you can manage it yourself.
If you are using Gmail from several years, you might have lots of unread emails are there. However, it will not create any problem but seeing a lot of unread messages in inbox is annoying. If you want to mark all the as read, you must go through the lots of pagination.
Lightsail is an amazon web service that provides you server space with your desired OS to host websites and other applications. It is simply a hosting service that includes everything you need to launch a website – Virtual Machine, Containers, Databases, CDN, Load balancers, DNS Management, Network Firewall, etc.