Backup not functioning

First, you need to provide a complete detail of the problem, when it is happening, what software is used, what error messages, if any, etc. We cannot help you, blindly.

Please read Writing an effective Apple Support Communities question. We are here to help. We are all users. We are not mind-readers nor clairvoyants. We only know what you write down and tell us. Be specific and thorough. Try to write clearly. Think about what you want to say before you write it down, then re-read it to see if it makes sense. We need the following at a minimum:

• What specific product model do you have? Avoid just saying, "iPhone or Mac," because that doesn't describe it uniquely.
• Tell us the version of iOS or Mac OS that you have installed on your machine.
• Provide a short but complete summary of your question, problem, or issue. (No complaints, please.)
• Give us all the details of your question, problem, or issue. Make your descriptions clear and precise but don't be wordy. Like Joe Friday used to say, "Just the facts." Be sure you provide any other details that we should know.
• Detail what you have tried, so far, to solve your problem even if it's "nothing."
• Provide images/snapshots appropriate to your descriptions. Pictures are worth 1,000 words.

Note: If English is not your native language, please let us know. Perhaps you would be better served by posting in your native language. If you do, then understand that getting a reply may take more time. Most of the helpers are native English speakers but some of us are bi- or multi-lingual. Unfortunately, English is my only language. I am able to use translators if I know what your native language is. However, I will be slower in responding.

You need to create a new Backup for Catalina as Catalina does not support previous Time Machine backups.