Creality CR10 PRO Z offset problem

Hi.I got my CR10 PRO in 2019, and though the feature "Auto leveling" didn't live up to the hype i thought it would be, it worked.Now it has been sitting for about a year. For another project i got a resin printer and also needed some extrution prints, so i fired up my CR10 "PRO".The problem is that i do all the bed leveling settings, but when i print it uses the Z0(~2,1 mm above the surface) as Z offset. It has also dissregardedZ0 and pushed down in to the print bed with the manual down command. I managed to set the Z offset manually once and it printed, but the next printstarted at Z0 again. In my latest test I noticed that using M500 and restarting the machine, it won't keep the setting. Z offset is 0 after power off.I'v googled for a firmware update, but Creality only offers one for the BLTouch update. And the links to firmware i found on various sites are removed.Any sort of help is highly appreciated.Happy printing!BRBNCZ