Hi @mickspawn a couple things to try.
Go to Preferences > Technology Previews... and check "Disable Native Canvas" - then restart Photoshop. Does the problem still occur?
If not, let's make sure we're in a default state and there are no stale settings somewhere:
Restore your preferences using this manual method:
https://helpx.adobe.com/photoshop/using/preferences.html#Manually
Does it work correctly?
If that doesn't solve it, you can quit Photoshop and put the Settings folder back.
It may help if we could see your Photoshop System Info. Launch Photoshop, and select Help >System Info...and copy/paste the text in a reply.
Thank you,