After checking with all linters of a large project - the directory .ruff_cache has a large size and a huge number of files inside. The first load of PyCharm slows down at the stage of indexing all the files.

The volume of lines in all files:

$ ( find src apps -name '*.py' -print0 | xargs -0 cat ) | wc -l
  979136

Cache directory size:

$ du -h .ruff_cache
1,5G	.ruff_cache/content
1,5G	.ruff_cache

Number of files in the cache directory:

ls -1 .ruff_cache/content | wc -l
  319586

As a quick fix, I excluded directory .ruff_cache using the context menu: «Mark Directory as -> Excluded».

But it doesn't seem to be ok if the cache doesn't clear itself.

PS: MacBook Pro Intel Core i9 with SSD