Have you dehydrated the filament? To me your issues look like typical moist filament problems. PETG is notorious for being hygroscopic, and I have found that Snapmaker’s PETG is additionally one of the worst for it. Of the 3 rolls of SM PETG that I have used, all 3 needed significant drying to make them even remotely usable, and even then they still had a LOT of moisture related problems. I have had no such issues from brands such as Overture and Polymaker, and I have printed more PETG from the two of them than all other brands and filament types combined.
Additionally, I print PETG at temps of 245C/80C and speeds not to exceed 40mm/s, but you need to be cognizant of your hotend if you are using a stock one; the PTFE liner in the hotend will eventually start to degrade at what are typical PETG print temps. More on that here: Hot End Clogs - The How & Why
Consider e-steps, flow, linear advance, and retraction calibrations a requirement for PETG to reduce stringing and surface artifacts; it loves to highlight and exaggerate any deficiencies in your tuning. It’s a very unforgiving filament, but once it is dialed-in, it can be wonderful.