Certified GKH Gardening Expert
22 days is on the long end of their germination time. In proper conditions, they should germinate in under a week. You may need to adjust temperature, humidity, or soil moisture in order to achieve proper germination rates.
It could be that the cultivar that is germinating for you is a little more hardy, and will tolerate less than ideal conditions. Since these do germinate in your area, you may want to put your focus into them.
This article will help you to germinate the seeds:https://www.gardeningknowhow.com/ornamental/flowers/desert-rose/desert-rose-propagation.htm