It is still hidden, but one of the reasons why the native Linux version is better than Proton.

https://factorio.com/blog/post/fff-408

Asynchronous saving

Many of you might not be aware that Factorio has support for saving your game in the background, without freezing while it does so. This feature is tucked away in the hidden settings and only works on macOS and Linux. This is one great example of taking advantage of a platform’s features to benefit the game, which would not be available to us if we simply went through Proton.

Asynchronous saving works by using the fork syscall to essentially duplicate the game. The primary instance - the one you interact with - continues playing, but the newly forked child runs the saving process then exits on completion. I have used it for many years and have never had issues, but the setting remains hidden because there are a few unsolved problems with it and it requires a significant amount of RAM to work.

I would love to promote this feature away from its hidden status in 2.0. If you are playing on Linux or macOS, please enable asynchronous saving (ctrl+alt+click Settings -> “The rest” -> non-blocking-saving) and report any issues you find. I am particularly interested in reproducing a seemingly random freeze that occurs at the end of the process. Thank you in advance!