Cursor and keyboard lag

All of a sudden my iMac cursor is slow/lagging when using the mouse. When I type it’s even worse adding in lots of ‘spaces’ even when I only pressed the space bar once or it’ll randomly display the options to add a foreign character.

I’ve reset pram, booted in safe mode (still occurs), restored using time machine to a time when it wasn’t occurring (but now does). It is very annoying. Any advice please.

iMac 3.5GHz i7

Lots of ram

1TB SSD (approx 1/2 free)

OSX 10.13.6