I exchanged some email with Tualatin Hills Park & Rec District (THPRD) last year - they indicated a pretty enlightened attitude about flying in the district parks. At some point they realized drones weren’t a nuisance use, and revised their regs to allow flying at almost all parks when not interfering with other users. Avoid the Nature Park though… and of course you want a location away from people.
THPRD includes soccer fields & etc., plenty of room for learning and practice.
They also sent me to the west side (off SW 184th) of Arnold Park, where they have an agreement with a local FPV club. I found plenty of room for some practice just to the north of where the FPV-ers had set up their gates. Nice people.