I personally prefer to access theme files via Filezilla instead of the theme editor because then I can maintain backup versions and use my favorite code editor. I also fear introducing an error with the theme editor which crashes the site and prevents access to the editor to fix the error. With backups and Filezilla it’s quick and easy to revert any introduced errors.
But with any classic theme you should have access to the theme editor. With block themes the menu item is not available but I think manually entering the /wp-admin/theme-editor.php URL would still work (unverified).
The one reason I know of why the theme editor would not appear with a classic theme is if the constant DISALLOW_FILE_EDIT is defined as true somewhere, usually in wp-config.php. But could be defined elsewhere such as by a theme or plugin.
