Well done with the downgrading!
I can help you continue, no problem, but a quick word or two about what’s in store for this device would be good if you have the time.
I know that there is a build in testing at the moment for R, so in the near future this device may be moving on to R. In addition to that there are a number of other one plus devices moving on to R this week.
Yourself and many other oneplus users are going to have to install stock android 11 before flashing e OS R.
I don’t know how easy it is to return to stock after flashing a custom rom but I’ll have to find out in order to help a friend of mine who has a oneplus 6 running e!
I’ll post again in a few minutes with some instructions for flashing with e-recovery.