Shimano R7020 shifter broken - no audible click when shifting
Thanks for the responses. Spent some more time looking at the problem and managed to solve it!
One end of the small spring seen in the centre of the picture fits through a small hole to keep it in place. This spring originally had no tension on it and seemed broken.
The other end of the spring had somehow slipped past the silver flange and was on the wrong side of it. This end of the spring has a small piece that should put pressure on the silver flange and only allows it to move slightly off the cog.
Once I had worked out how to get the spring in the right place it all works fine.
The way I did it was to pull the end visible out of the hole so the whole spring rotates. Find the other end of it and squeeze it past the silver flange so it rests on top. It is flexible so quite easy to do.
The larger end of the spring is then under tension and you can pull it back up and fit it through the hole. This is a bit fiddly but achievable.
Photo of the finished result with yellow arrow pointing to large end of spring going through hole and white arrow pointing to other smaller end resting on silver flange under tension.
Hopefully it may help somebody else. I wonder how many shifters have been discarded because of this small spring!