This is one of those models made for the Russian market. The latest update is from January of last year 2022-01-20_19-37_2.1.2_5b90d57 (can be downloaded at:
https://onyx-boox.ru/support/boox_monte-cristo5).
Just download the file and transfer it to the Boox device. Then go update it in the settings. Do a factory reset afterwards.
The instructions also state to do a battery recalibration.