Here are some steps you can take to resolve this error:
1. Clear the generated code directory by running the following command in your Magento 2.3.5 root directory:
rm -rf generated/
2. Run the compilation process again by running the following command:
php bin/magento setup:di:compile
3. If the error persists, try running the following commands in your Magento 2.3.5 root directory:
This will update any dependencies that may be causing the issue.
4. If none of the above steps work, try disabling any third-party modules that may be causing the issue. To do this, run the following command:
php bin/magento module:disable Vendor_Module
Replace "Vendor_Module" with the name of the module that you suspect is causing the issue.
After disabling the module, clear the generated code directory and run the compilation process again.
Hopefully, one of these steps will resolve the "Class SynchronizeFilesInterface does not exist!" error in Magento 2.3.5.