fluxcore on 0.75mm

[G1zm0]

@G1zm0 the machine you have should be fine for filling holes in relatively thin sheet metal in the right hands. As @eddie49 says it isn't clear what exactly it is you are doing, you mention spot welding but it does appear to be more filling holes? At a guess I'd suggest your stick out is too long and you might be struggling to see the puddle if you are using the fixed shade handheld mask that came with the machine. A bit more info about what you are trying to achieve and what you have tried already would be good..

I'm filling in the sporwelds that got drilled straight through , then I want to put new panel on welding to that part

 

[RonMig]

0.6mm gasless/fluxcore wire Can weld very thin metal but I find it has to be with fast-tacks / short-bursts.
But the weld size probably will be too small to fill an 8mm hole without going too hot & burn-through.
Going round the edges to fill-in can work but is unlikely to be neat (unless you're very good...), then you will grind-down to a perilously-thin sheet and probably make more holes.
Don't ask how I know this....

I suggest you -
a) Stick with the 0.9mm wire
b) turn the heat/wire speed UP slightly, maybe to around 1.2mm on the Lidl synergic control
c) and work Faster - like 1/2 second bursts, 1 second apart.

and Practice, on scrap, first.

I did my Disco sills and inner wings last year with my same Lidl Mig and am happy with the result