Hi @konsos I don’t know if you have searched the forum for teracube + easy-installer but there are two of you in what looks from here a similar position. Please compare with Installation stuck in recovery mode after easy-installation.
Teracube has quite recently returned to the Easy Installer list, having been removed at least partly due to too many failures.
I had a Super partition device once which I liberated to /e/; I remember now that one thing I found worked was to flash the device in one go. Of course Easy Installer aims to do just that as do the manual instructions https://doc.e.foundation/devices/emerald/install.
The reason I mention this is that if the Teracube is similar, any breakdown in the Easy Installer flow could be very hard to know or advise how to get out of.
You say your Teracube just arrived, so I have assumed it is the newer “2021” model. Please can you confirm that we are all talking about the same device. 
Caution: Before moving forward, ensure your device is a Teracube 2e (2021). Please look at the serial number under the battery or dial *#06#. If the serial number starts with 2021 (ex: 202111T2Exxxxxx), you are at the right place!
I an not going to suggest anything experimental, but please try reading as much as you can. Previous answers, linked indirectly from my first link above might give you an insight. (I do not want to highlight any one case as I cannot tell if you all have some significant thing in common and I don’t want to misdirect.)
If you decide on a fresh start you have the option to flash the “Factory” ROM with a powerful tool (SP Flash) which needs Windows. Beware it is especially powerful, please read the guide carefully.
https://community.myteracube.com/t/advanced-installing-factory-android-image-w-sp-flash/1003
Note also the “Update: new process” linked in the first lines.