Found a quote, had to use the anglicized spelling though.

https://www.vanityfair.com/culture/2011/08/heller-201108

"The Czech writer Arnošt Lustig claimed that Heller had told him at a New York party for Milos Forman in the late 1960s that he couldn’t have written Catch-22 without first reading Jaroslav Hašek’s unfinished World War I satire, The Good Soldier Schweik. "

Germanized, really.

there are some references in catch-22 and its follow up Closing time.

I was really surprised by Closing Time. I forget all the details of it, but I remember finding it just relentlessly depressing. The only degree to which I thought it worked was, it really emphasized the extent to which we really don’t need to know what happens to characters after the story is done, it is better if we just imagine they go on to have their lives.

Same. It was so heavy compared to catch-22. But I am not sure the aging perspective could have been written any different.