Gentoo has many advantages and is the ultimate choice for many Linux users. However, Gentoo is a bit of a pain to upgrade, especially if it has not been upgraded for a long time and there are many errors that can prevent you from entering the upgrade process.
For example, there are many errors when upgrading the world. The USE changes are recommended to be merged manually into package.use. perl-related errors can usually be resolved with the perl-cleaner tool. The remaining dependencies are usually still very difficult to resolve.
My solution is to copy the printed upgrade list into a file and use a script that forces the installation to go in order.
Once this is done, the system will be almost up to date.
Additionally, try using the emerge upgrade world command again. Even if there are still errors, they will be easier to locate and fix.
The script tool: gentoo-fxck.sh, only one parameter: the path to the text list file.
Sometimes upgrading the world only reports errors and does not print the upgrade list.
You can try upgrading some software first. Any time that emerge has some errors and there is a printed upgrade list, you can use the script to upgrade.