Based on what I'm reading I think I will also try increasing Z offset to .2 on my next PETG test print.
If I can't get the PEI plate cleaned up I'll just order another, and use the damaged one as a sacrificial lamb for additional PETG testing. Hopefully I can clean it off, don't like to waste things...
First try at 61 degrees yielded some initial small success, but overall not much came off after that. I'm heating to 68 degrees now to see how that goes.
68 degrees didn't help, not coming off at all.
Someone posted this intereseting solution...may try this as a last resort...
PROBLEM: broke off the 3d print supports but the first layer didn't came off with it. I've tried a lot of thing and a knife was really the only thing that worked until this point.
SOLUTION: Print something on top of IT to make IT stick to IT and then remove IT.
Print about 4-layer sheet of PETG on top of the remaining sticked filament (use some ugly one as it's going to be thrown away)
Let it cool off.
Remove the 4-layer printed sheet from the PEI and enjoy the maginc.
If the Z offset is too small, it does adhere much too well. Increasing the Z offset too much and it doesn't adhere. Using a folded sheet of paper to set the Z offset and then increase one of the smallest units you can seems to have worked for me to be the best for both adhesion and release of PET-G. I'm using a HICTOP PEI sheet which is on a metal base with a magnetic sheet to hold it to the bed. https://www.amazon.com/HICTOP-Flexible-Platform-235x235mm-V2οΌEnder-3/dp/B08PFHBR2D/
The Sovol SV05 comes w/a built-in magnetic bed and flexible build plate like below:
It's not PEI, not sure what it is, frankly. Works well, but not as well as the Creality PEI sheet on metal base worked (until I glued PETG on part of it).