If I purchase an Amazon Lightsail product, is it compatible with my existing WordPress or do I need to open a new WordPress and start production again?

If it is Amazon lightsail, you need to see the difference in the environment during installation.
If the environment is different from the new base, a conflict error may occur.
It’s okay if you’re good at migration and check it out.
First, you need to know the site and the version to determine compatibility and development direction.
Lightsail allows you to directly modify the server configuration itself. So, if you migrate while keeping the configuration as similar to the existing server environment as possible, problems can be minimized.
For example, differences in PHP and DB versions come first, but in the case of Lightsail, there are also differences in OS.
You need to check this first to get the answer.
If you have always kept Warp up to date and used commonly used themes or plugins, even if the PHP version or DB version of the new server is a little higher than the existing server, the migration can be successful by checking compatibility.
So the priority is to analyze the environment of the previous server.