Retek Which keyboard app is this? It doesn't look like the stock GrapheneOS Keyboard. The menu entries and interface look different from what I'm seeing on my phone.
The personal dictionary for the GrapheneOS Keyboard does get backed up when doing system backups. I confirmed this on my own devices. Not sure if any of the non-default checkboxes need to be ticked in Settings > System > Backup. The options on my device are all enabled, except "Backup my files".