Well that is a possibility, but the install instructions are written for T and the R install instructions are no longer shown. Although a different device I made the same comment in this thread OnePlus 8 Pro additional partition required but lacks expected images.
Here are Lineage instructions which “bridge” the Android 11 - Android 13 install methods. https://lineageosroms.com/instantnoodle/.
If you choose Android 11 (R) MSM and copy-partition would be a sound way to clean up the device in case it was compromised by the attempted downgrade.
Many on the forum here are using dev builds for their daily driver, but I understand how you might be attracted to the stable label.