Exterior wall damaged - what should I do

is that the final job? Not really sure what that is supposed to be achieving, that’s not the actual fibre cable it it? If you paid for install I’d be back on to them saying they’ve damaged it and it needs a repair.

In principle a simple ready mix external filler would do fine but as per earlier comments this doesn’t look like a final job.

If it is that guy should be fired on the spot.

Looks like most jobs I've seen carried out by Eir or similar. Lash it in, get on to the next job.

What does the finished job look like?
Is that external insulation or plaster on block finish?
Your pic is off a hole before any repair was made, and that looks like a cable pull as opposed to the actual fibre line.
Hard to give an opinion unless you show the final job.

A piece breaking off like that isn't a major issue & I wouldn't fault the engineer. There should be a pipe / ducting going through the wall and the cable goes inside the pipe. The outside of the pipe (inside the wall) should be filled with expanding foam. Every hole made by tradesmen in an outside wall should be made airtight. They should be assuming that every home is airtight.

That looks external insulation? Which in some cases I've seen you could push your finger through it it's that spongy.

When ever the cable jobs finished and if it is external insulation I'd use some expanding exterior foam to fill and finish it.

Abysmal work. The cable isn't even clipped straight. But this is how a lot of these installers do the job.

Buy nothing, make a compliant about the install to the service provider and ask them to rectify it to your satisfaction and at their cost. It's a very poor job and no one could possibly suggest this is acceptable.

Can you post a pic of the fibre coming out of the conduit lower down?

I'd probably find some half moon trunking to cover it up. I think that stuff can be screwed into the wall in a way that the fixings are covered. Paint over it if necessary.

As for the splodgy hole, ugh. I'd want that gunk out and replaced with proper masonry filler e.g. Toupret.

He gets paid to do the job, so he is a professional. He's just not very good at his job.

that’s not the definition of a professional

Much as this pedantry is unproductive, "professional" as a adjective implies competence, whereas "professional" as a noun implies only that it's their job.

So you can have an unprofessional professional and a professional amateur 😀