Typing text does not behave correctly since Big Sur update

Since upgrading to Big Sur, any time I try to type anything across any application I get mysterious rogue words or characters. As I've typed his post, I've had to stop and delete things over a dozen times.

It appears to be duplicating characters that have already been typed, or at least similar things that have been typed already.

I've added a screen shot from Text Edit with the mysterious duplication text highlighted in yellow:

Any help would be great.

Thanks!