I simply stopped even trying to use sleep mode because I had some issues and many people responded to my inquiries telling me that it’s always been spotty in Linux. I have one laptop that goes into sleep mode perfectly fine when I close the lid, and wakes perfectly when I open it. That’s an Asus x202e with Pop!OS. Then I have an older HP Elitebook with Elementary OS that goes into sleep mode when I close the lid, but in order to resume, I have to open the lid and then press the power button to wake. And finally my new ASUS zenbook with Kubuntu would go into sleep and never be able to wake no matter what, and required a hardware forced shutdown. So that’s my main system and I simply disabled sleep. When I close the lid it just shuts off the display. It’s actually not bad because I can leave something running and close it, and it continues the tasks.
These days the computers use such less power than they used to, so it’s not really the biggest necessity to use sleep mode.