Hi @wally
thank you for the feedback.
Smartphone purchased in EU (Bulgaria) for experiments, OxygenOS v11 and v10 worked perfectly.
EU_BE89BA has been used to downgrade from v11 to v10.
Actually there was a lot of problems during UT install (a lot of UT Installer restarts and device reboots), but in the end UT has been installed.
I will try to repeat the installation process and report errors via the UT Installer form.