How can I get the arrow keys back in the centre of the SwiftKey keyboard?

You can reinstall an older version, try one of the following sites to download.

• APKMirror


• APK4Fun


• APKPure

Swiftkey version 7.6.5.7 seems to be the latest version that has the arrow key + thumb keyboard functionality available.
You can download and install the linked .apk file.
After that you need to configure the Google Play store to not auto-update Swiftkey by following these steps:

1. Open Google Play store


2. Navigate to the Swiftkey app


3. Click the three dots in the upper right


4. Uncheck the box Enable auto-update ⬜.

_{Disclaimer: I take no responsibility for the apk's on these site.}