OnePlus is an OEM that has come to official ingress-protection ratings relatively late in its life cycle. However, it bowed to consumer pressure and provided the IP68 spec in its early-2020 flagship, the 8 Pro. Now, a reliable leaker asserts that its successor is getting the same.
https://www.notebookcheck.net/The-OnePlus-9-Pro-will-be-IP68-certified-whereas-the-9-and-9E-will-not.508881.0.html
That's 0 growth for OnePlus..The 8 Pro also had IP68 rating last year. It would have been remarkable if they had provided some rating on the non-Pro or they could have launched the 8T with IP68.
The S20 & S20 FE have IP68 and the S20 FE is already cheaper than 8T..plus you can even get S20 at a pretty low price on one of those sales.
Considering this it'll be smarter to buy the S21 at a sale with IP68 rating, then go for the OnePlus 9..