This looks like an index of Mir books, without any additional sorting or curation. You probably can get a good education on many topics out of these, but also waste significant time on reading out-of-date and out-of-order texts. Someone experienced could make this a lot more useful by proposing a reading order and giving some sort of evaluations of importance and quality.
And keep in mind that these are from the pre-1990 USSR, so don't expect any modern maths or CS.
on the other hand, one could argue, for basic stuff it would be ok, but I agree, it is not really well curated, there are some books, which are duplicate
This is mostly archive.org links. Some of them still work (you can actually download the scanned book) but lots, maybe most, are unavailable due to the copyright settlement. You can still see the cover and metadata and maybe some sample pages.
First impression from this list is that Russia has a lot of mathematicians!
From the list, I have only read What is Mathematics? by Courant, which is a well-known and excellent book. I’d add Princeton Companion to Mathematics as a more advanced version, and Mathematical Methods in the Physical Sciences by Mary Boas as a more detailed alternative to What is Mathematics, to the list. Other titles on the list, such as those on probability or linear algebra, are perhaps less well-known.