Thank you for your replies.
The manual is here: (cites 2021, but is same as 2020) https://techinfo.subaru.com/stis/doc/ownerManual/MSA5B2105A_STIS.pdf
page 46:
ENGINE OIL
Use 5w30 synthetic, with one of the following specifications:
• API classification SN or SN PLUS with the words “RESOURCE...