The springs and shock absorbers work with all tyre sizes. The springs and shock absorbers aren't tuned for the tyre size that the car is fitted with, but the weight of the vehicle.
Skoda fit the same springs and shock absorbers irrespective of what tyre sizes are fitted, whether it's 195/65R15, 195/60R16, 205/55R16, 205/50R17, 205/45R18, etc.
Running different outside diameter tyres front and rear isn't a good idea, especially when the difference is 3.4% as shown in the chart below.
Outside diameter of tyres
215/40R18 629.2mm
215/45R18 650.7mm (3.4% bigger outside diameter compared to 215/40R18)
If you're looking for a quiet, comfortable ride, summer touring tyres in size 205/50R17 fitted to the standard 6.5Jx17 ET40 rims would make more sense. Although not quite in the same league for sportiness as 205/45R18 fitted to the standard 7Jx18 ET39 rims, it's still more sporty than 205/55R16 fitted to the standard 6Jx16 ET38 rims.
Another benefit of moving up to a 50 aspect ratio is that the tyres' sidewalls tend to bulge out more from the rims, thereby providing much better protection from kerbing damage.
Michelin Primacy 4+ 205/50R17 89V (Euro label C A 69dB)
https://www.mytyres.co.uk/rshop/tyre/Michelin/Primacy-4_/205-50-R17-89V/D-126315
6.5Jx17 ET40 5/100 57.1 alloy rims
https://eshop.skoda-auto.cz/cs_CZ/alu-kolo-propus-17-scala-kamiq/p/654071497K+FL8
Actual inflated width of tyre
205/55R16 fitted to 6J rim 208mm
205/50R17 fitted to 6.5J rim 214mm
205/45R18 fitted to 7J rim 206mm
215/45R18 fitted to 7J rim 213mm
Actual width of rim (assumes actual width is 24mm wider than J width)
6J rim 176.4mm
6.5J rim 189.1mm
7J rim 201.8mm
As you can see in the chart below, the sidewalls of the 55 and 50 aspect ratio tyres (ie. 205/55R16 and 205/50R17) bulge out from their rims by 15.8mm and 12.45mm respectively. The sidewalls on the 205/45R18 bulge out from its rim by a shockingly low 2.1mm. Hence, 205/45R18 when fitted to a 7J rim provides very little rim protection from kerbing damage.
For the 215/45R18 tyre size fitted to a 7J rim...the sidewalls bulge out by 11.2mm, ie. 5.6mm each side. So still well short of the 205/55R16 and 205/50R17 fitted to their 6J and 6.5J rim widths.
How much wider tyre is than rim
205/55R16 is 31.6mm wider than 6J rim, ie. tyre bulges out by 15.8mm each side of rim
205/50R17 is 24.9mm wider than 6.5J rim, ie. tyre bulges out by 12.45mm each side of rim
205/45R18 is 4.2mm wider than 7J rim, ie. tyre bulges out by 2.1mm each side of rim
Another benefit of 17" rims compared to 18" rims is the reduction in unsprung weight. The 17" alloy rims might weigh about 10kg each, whereas the 18" alloy rims might weigh about 11.5kg each. So that's a 6kg reduction in rim weight, and 7.5kg if you include the weight of a matching spare wheel. 215/45R18 might also be a heavier tyre than 205/50R17...so that's yet more unsprung weight.