Dreaded Repeating Characters

This is an issue that I have seen pop up several times historically but for which there seems to be no definitive solution.

I use a Macbook Pro 15" 2016 target-screened to a 27" iMac and a magic keyboard 2 with numeric pad.

Randomly (but frequently) characters are duplicated whilst typing. This can be up to 4 characters, so something like 'Hi Anthony' could become 'Hi AAnthony' or Hi Anthonyhony.

Another variation is typing a word and the repeat happens part-way through the word and inserts a space, after which I complete typing the word: so 'randomly' could become 'rando randomly' .

Sometimes the repeat is almost instant and others maybe 1 second after typing the word.

This happens in pretty much any applications and with both the bluetooth and integral keyboards. I initially thought it was my old magic keyboard 1st edition so splashed out on a new one for no good reason!

This has only happened in my case since upgrading to Catalina - which I did from High Sierra. I have never experienced the issue before

I have tried the usual suggestions including resetting PRAM / NVRAM, SMC reset, turning off repeating keys and so on. Nothing makes any permanent difference.

I'm really finding it unacceptable that this fairly ancient problem hasn't been identified and squashed. It really should not be beyond Apple's capability to produce a computer that types properly! In typing this short post I have corrected seven duplications so far - as you can imagine it makes for a very frustrating experience.

Any thoughts welcome.