As the file properties show, it has not lost in size, but now it cannot be opened by the archiver; it reports a damaged header and an unexpected end of the archive. I tried to restore the archive using many programs, but all in vain. The last save was made 4 months ago, so everything that was done in 300 hours remains in the corrupted map. Yes, I know that I should have made extra saves, because it only takes a few seconds, but when you work with only one day off per month and have many other issues in life, it all becomes exhausting, and the chance of human error increases many times over. After three days of despair, it seems that nothing can be done, and there is a desire to simply abandon everything for an indefinite period. However, before that, I decided to write here, maybe someone knows a way to solve this problem.
I will leave two files; in the first case, it is the map before the recovery attempt, and in the second, after (now it can be opened with a text file)
