have you seen also the reply I got to my initial question? what I was missing was the fact that secure folder must be completely uninstalled not only the emm app uninstalled from secure folder. so when I did that in step 8 of my sequence INSTEAD of removing the app from secure folder everything went fine for me.Instructions are so unclear that it looks like it's been written by an autistic person who assumes everyone has the same knowledge as him.
I followed them to best of my ability but adhell is showing uninteractable gray screen.
1. Got the correct emm app
2. launch it in normal shell
3. from recents clear it
4. enable secure folder from settings
5. add emm to secure folder and launch from there
6. clear it from recents again
7. Uninstall emm from normal system
8. open secure folder and remove that emm app from the secure folder
9. in secure folder hi,t three dots, settings/more/uninstall, keep the default "take media out" or whatever it's in English checked
10. Install adhell
11. without opening it, enable it in device admin apps
12. Boom, grey screen
before retrying the sequence I uninstalled everything related to this process including my existing secure folder and rebooted the phone