Resolved! STM32G0 Reference Manual Typo (ADC-Oversampler)
RM0444 (Rev. 5 Nov 2020 - should be newest): Chapter 15.8 Oversampler: "N is defined using the OVFS[2:0] bits": this should say "OVSR[2:0]" bits. Chapter 15.12.3: Register ADC_CR Note for AD_EN: "set ADEN only when all bits of ADC_CR registers are 0"...