Hi Ellie2023_,
Thanks for contacting Apple Support Communities!
We understand that you're unable to use the arrow keys in Numbers on your Magic Keyboard Folio.
Are you able to use the arrow keys using software keyboard in Numbers?
We also see that you're running an earlier iPadOS version. You may also consider creating a backup of your iPad then update the iPadOS to iPadOS 16.2: Update your iPhone or iPad
"Update your iPhone or iPad wirelessly
- Back up your device using iCloud or your computer.
- Plug your device into power and connect to the internet with Wi-Fi.
- Go to Settings > General, then tap Software Update.
- If you see more than one software update option available, choose the one that you want to install.
- Tap Install Now. If you see Download and Install instead, tap it to download the update, enter your passcode, then tap Install Now. If you don't know your passcode, learn what to do."
We look forward to your reply.
Cheers!