If you want to create a Joomla backup manually, you will have a relatively high effort. However, a manual backup is also the safest option if you consider all important points. First, you need a secure connection to your web space to backup all folders and files on the server. Best is via SFTP. Second, you also need to pull a backup of the Joomla database to keep all text content, configurations and user data safe.
Backing up Joomla folders and files online:
The easiest way to create a manual backup of your online storage is to establish an (S)FTP connection in the usual manner and then copy the files and folders to the desired storage directory using drag-and-drop. Alternatively, you can select the files in most FTP clients such as the FileZilla used here and download them via the menu item of the same name: