I’ve used lightsail quite a bit. The problem with this, and any other auto/pre-installer is the packages are modified by the installer to get them to work in an automated way. This often leads to parts of a package, or the whole package being out of date. It can also lead to file permission problems and database structure differences. I have seen a lot of issues in the past simply because of these types of installers. Lightsail is a nice, cheap way of hosting, albeit with some oddities and a lack of support. All opinion, though.
What O would suggest here is to do what it says on the page and backup. Make sure you backup your file and your database. Akeeba backup is a free tool that can do this for you in just a coup,e of clicks.
When you have done that Go to the Database Fix page, by navigating to Extensions -> Manage -> Database in the backend of Joomla.
Fix and update your database and you should be good to go. Be aware though, the updating Joomla 3 to 4 can be problematic, usually due to outdated extensions. The backup will be your get out of a hole card here. I tend to take that backup to my desktop and run all the update work locally using a tool like WAMP or XAMPP. This way I do not affect my life site.
Belt and braces, use the built in backup tool in Lightsail to take a current snapshot of your instance before yo start, that way you have another quick way of restoring if it doesn’t go as planned
