Question on carry on bags for Wizz Air

Wizz Air policy is 40x30x20 for 1 free carry on bag.

Is there anyone who has travelled with a slightly bigger bag than this and had no issues with Wizz Air?

Some people might have got away with a bigger bag than they're strictly allowed (I've personally not flown with Wizz Air), but that doesn't necessarily mean that you will.

There's some information here: https://wizzair.com/en-gb/information-and-services/travel-information/baggage in the section "What happens if my carry-on bag (40 x 30 x 20 cm) doesn't fit in the sizer?":

"For passengers without WIZZ Priority and with a carry-on bag, which exceeds 40 x 30 x 20 cm, an oversize bag fee of 30 EURO will be charged at the gate. In case such bag does not exceed 55 x 40 x 23 cm, the bag can be taken onboard, assuming there is space in the cabin overhead compartment. In case there is no space, the bag will be taken to the aircraft cargo hold. Passengers can remove their personal items from bags going to the cargo hold."

Bear in mind that you might get away with it; or you might get away with it in one direction but not the other; or you might be charged in both directions (assuming you're on a return trip).

(I'd argue that a 45x36x20 bag is not just "slightly larger" than 40x30x20.)

You will almost certainly get charged. I used to work for Flybe customer service way back when - it was openly stated among the staff that a major income stream was from the charges for checking baggage on the day from people who tried to bring too big a bag and it didn't fit for the overhead. It's by design. They used to make you stick your bag in a measuring thing before checking in and if it didn't fit "naturally" (i.e. no trying to cram it in there) you'd have to check it - and pay the on the day checked baggage fee.