I have been living in Korea on an F-4 visa since 2021. It's a convenient visa, and here's my honest fail: I didn't know that you need to notify the immigration service when changing jobs.

I knew that for many visas such notification was mandatory, but for some reason, I thought it wasn't required for F-visas, or 
that the employer handled it.

Then I saw an announcement on HiKorea dated 19.12.2025 about the implementation of a mandatory online notification system for 
foreigners' employment. I was confused by the term “영리활동”: the translator rendered it as "commercial activity," and I thought it only applied to those running a business.
But after calling 1345, they explained to me: for the purposes of this obligation, “영리활동” = any paid work/activity, including employment and self-employment. This means changing employers (and other work-related changes) is subject to notification.

In my case, I am finishing my job on the 31st and will be temporarily unemployed afterward - in such a situation, a separate notification of "I am not working" is usually not required.
But when I get a new job, I will need to submit a notification through HiKorea (and during the pilot period, submission in paper form by visiting the immigration office is also allowed).

I have prepared a detailed description of the system and a link to the source for you. If you need a separate tutorial on "how to apply 
online," please write in the comments - I will create a post in Russian.

If you haven't found the answer to your question in this post, I highly recommend clarifying your specific situation by calling 1345 or 
at your local immigration office, as decisions for specific cases depend on the details.