I recently bought a 2006 Ford Focus MK2 Petrol 1.8, a few weeks ago the oil light came on, I refilled and now every 5-7 days I have to put in approx 4litres of oil. There is blue smoke coming out of the exhaust which I have been told could be due to faulty piston rings. Around a week ago, whilst working, the oil light came on and I had to drive around for around an hour with it on before I was able to top it back up. I was advised to try a thicker oil, the manual states to use 5w30 but I put in 10w40 in hopes that it wouldn't burn as quick. But since I have been getting a fast ticking/tapping noise when driving about 3k RPM or when driving at a constant speed above 2k RPM. There's no noise at idle, or whilst I'm accelerating/decelerating. Does anyone have any advice on what's making this noise?

By the time the oil light comes on, it's generally too late and you've caused serious engine damage. 4 litres of oil every week is a lot, eventually your engine just won't turn over if you carry on like this.

The tapping noise will be oil starved lifters at the top of the engine. This will get worse as time goes on.

You may be lucky and only need the cylinder head refurbishing with new valves/stem seals. The cost of this is probably not much less than a new engine, and considering you've starved the rest of the engine multiple times (by letting the oil light comes on) I'd be replacing the lot.

Piston rings are a common issue on the 1.8 petrol and probably why the previous owner sold it.  It'll never pass another MOT emissions test.

Putting thicker oil in isn't a great idea as you'll get less lubrication, especially when cold.  Oil through the cat will have ruined the efficiency of that as well.  Best option is to cut your losses and buy something else imo.