I freely admit that I no next to nothing about gardening in general (and absolutely nothing at all about growing cucumbers) but that nice Mr Google finds a vast number of links all agreeing with your conjecture that it's a pollination problem.
Digging a bit deeper though, to work out where you've been going wrong, has proved a bit trickier but I wonderd if you realise that you must only use
fresh pollen, as it's only viable for just one day.
Quote:
"Learning to recognize the difference between male and female flowers is the most important aspect of hand pollination of cucumbers. Both grow on the same plant. Male flowers differ in appearance from female flowers by having shorter stems and growing in clusters of three to five, while the female flower blooms singly; alone, one per stalk. Female flowers contain a small ovary in the center; male flowers lack this. The female flower will have a small fruit at the base of her stem. When hand pollinating cucumbers, use only fresh male flowers. Flowers open in the morning and pollen is only viable during that day.
Locate the yellow pollen inside of male flowers. Remove the pollen with a small, clean artist’s brush or break the flower off and carefully remove the petals. Roll the yellow pollen on the male anther onto the stigma in the center of the female flower. Pollen is sticky, so expect cucumber plant pollination to be a tedious and painstaking process. One male anther can pollinate several females. When completed, you have accomplished cucumber plant pollination. This process should be repeated for effective hand pollination of cucumber."
Source:
https://www.gardeningknowhow.com/edible/vegetables/cucumber/hand-pollinating-cucumbers.htm
Youtube also seems to have loads of videos demonstrating the technique.