G5 Inspiron 5090 cooliing

My wife's G5 5090, with a Core i7 9700K CPU, was a pretty cool machine when it was new (November 2019), but it has a couple of faults.

One of them is the cooling system--if I add a second task to what I'm doing, the fan goes off like a jet engine. The AWCC is set to "Quiet Mode." My wife does a fair amount of gaming, but this happens even when there are no games running. There's no overclocking or stuff like that.

I see that there are several comments and videos about improving the 5090's cooling system, some of them very elaborate. My question is, would I get a significant improvement (i.e., reducing fan noise) by replacing the current 80mm fan with a bigger one, or adding another fan or two, or do would I have to go to the lengths of a new and improved CPU heat sink? a new CPU cooler? I'm looking for a fairly low-cost solution.

Any suggestions gratefully received. Many thanks.