I wasn't aware they stopped publishing them so I didn't back it up, but I can't say I really care for my use case. The only reason I'd need it is to resell the phone, but my plan is to use it until it's either broken beyond repair or backporting new Android versions becomes impossible, at which point nobody would buy it anyways.
I agree the OP6 is great (my girlfriend is still using hers), but I was still on my OP 3 like a year ago, until future ROM updates were deemed impossible thanks to Qualcomm binary blobs.
It's a real shame it's all over now. The OP 9 Pro was the last OnePlus phone made in their old way (or close to it) - not too expensive, well built, close to stock ROM, easy to reflash, decently repairable. Hopefully it lasts me as long as the 3 did because currently I don't see anything else like that on the market.