I’ve had something similar before – some community plugin made a mess of the mobile sidebar.
If you are comfortable, close Obsidian, rename the <vault-name>/.obsidian/workspace-mobile.json file, and restart. The mobile workspace will be reset to the default layout.
If you sync your vault with iCloud Drive, you can rename the file on your desktop and have the change sync over. If you use another sync method or are phone-only, you can use an app like Taio or Textastic on iOS to rename the file.
Before you try the above though, I’d follow all the troubleshooting guide. It may be a plugin or (less likely) a theme causing the issue.