I had to manually flash firmwares from OOS 12.C65.
They are available at https://android.googleapis.com/packages/ota-api/package/490bb705386df0e2f1b1ed4c3fa6483c045a7343.zip (OOS 12.C66 is an incremental OTA that doesn’t adds new blobs)
Need to enter special fastbootd mode to flash (fastboot reboot fastboot), and then flash:
fastboot flash --slot=all abl abl.img
fastboot flash --slot=all aop aop.img
fastboot flash --slot=all bluetooth bluetooth.img
fastboot flash --slot=all cpucp cpucp.img
fastboot flash --slot=all devcfg devcfg.img
fastboot flash --slot=all dsp dsp.img
fastboot flash --slot=all engineering_cdt engineering_cdt.img
fastboot flash --slot=all featenabler featenabler.img
fastboot flash --slot=all hyp hyp.img
fastboot flash --slot=all imagefv imagefv.img
fastboot flash --slot=all keymaster keymaster.img
fastboot flash --slot=all modem modem.img
fastboot flash --slot=all multiimgoem multiimgoem.img
fastboot flash --slot=all oplus_sec oplus_sec.img
fastboot flash --slot=all oplusstanvbk oplusstanvbk.img
fastboot flash --slot=all qupfw qupfw.img
fastboot flash --slot=all qweslicstore qweslicstore.img
fastboot flash --slot=all shrm shrm.img
fastboot flash --slot=all splash splash.img
fastboot flash --slot=all tz tz.img
fastboot flash --slot=all uefisecapp uefisecapp.img
fastboot flash --slot=all xbl_config xbl_config.img
fastboot flash --slot=all xbl xbl.img