Myrtle problem

I have this plant, it came to me with serious black spot. Got rid of that, but this year it's looking very sad, red leaves, no new growth. Is it a lost cause or any recommendations for recovery please?

 

There are only a few red leaves showing on your picture. I suspect they are simply old leaves which will fall and be replaced. Even evergreens loose leaves they just do it more slowly and some less obviously than others. Is it in the ground or a pot? If the latter the lack of growth may be because it’s still settling in. If a pot, maybe it needs a refresh of the compost or feed.

 

Are you sure it's a myrtle?

Here's a pic of mine that I've had for about 20 years - I'm not sure the leaves on yours look quite right for a myrtle - or maybe yours is a different variety - not sure...

 

That looks more like a Cotoneaster?
There are lots of things it could be, tbh, I'm not a shrub expert. But I do have a myrtle and several Cotoneaster, and it looks much more like the latter.

 

My first thought when I saw the pic was Star Jasmine (trachelospermum jasminoides) - which is well-known for getting red leaves over winter and is normal for them.

 

Took some photos. The Cotoneaster is looking rather glossier than usual due to lots of new leaves, but I found some manky ones! Also on myrtle and Trachelospermum.