I need to find some information in old userman logs, which are backed up in .umb files. Unfortunately, this format is not readable. Is it possible to view them? Some kind of UMB viewer?

I've found some work-around - install UserManager on clean Mikrotik, upload UMB log file, load it and print it to file using:

ros code

/tool user-manager database load-logs name=userman-log.umb
/tool user-manager log print file=um.log

and download the log file to computer to analyze. It is not very efficient way, but how to do that better?

Sorry, you must restore one routerboard with RouterOS 4.16 and import the umb file, if are one backup of old user-manager.

If are new user-manager format, you must restore one routerboard with RouterOS 6.11 and import the umb file.

Yes, it is in the new format - I have done it as I wrote. I use script which save UMB backup and clear log at the beginning of each month and now I needed last few months to check some security issues. I think that some UMB log extractor or viewer would be very useful.

If you made backup inside user manager (also after you import the db... )
it create .tar file with inside sql3lite files.....

No, I didn't make any backups manually (inside User Manager). The strange thing is that after loading log from file (in terminal), User Manager doesn't show anything in his log.

User Manager is very strange indeed - there are some things that are duplicated - some of them are accessible from User Manager, some of them from terminal. Sometimes, these two are not the same and then various problems are appearing. Many old bugs are not fixed and Mikrotik stuff gives low priority to User Manager