I have a Galaxy A70 phone.
Eversince I converted to Android 10, I can't log into Galaxy Themes.
Everytime I try to open the theme page from Settings, I get an error code with this message: "Something went wrong. Try again later."
Check to see that your galaxy store is updated, you are also able to access themes through it. If you can download and manage themes through the store and not settings then we know that your setting may be the issue