On this page there is a link to a page with instructions for updating. In steps 4 and 5 of installing XML Scatter Firmware, it is said about an authentication file, but it is not in the folder shown. What can I do about it without bricking the tablet?

And thanx to Alldocube for link to wrong instruction - i got a brick

I unbricked it from bootloop using the SP MDT Tool and the latest firmware from this page and the file auth_sv5.auth (maybe the last file is not needed), and as a result I got a working Android 15

Hi, Eli C. i used this file auth_sv5.auth - https://mega.nz/file/pS5BBCDC#sDQtFxfPerjmxRVFYwoxj8EJMf74uwcR9El3tEPoPDQ (don't sure it`s needed) Also Alldocube support sent me link to SP_Flash_Tool_Selector_exe_Windows_v1.2216.00.000.zip (without auth-file)  https://mega.nz/file/pF9SV , but i already rebricked and installed android 15 with SP MDT Tool