Do I need to tell you about ongoing sick leave when I apply for a job?

AnswerYou are under no obligation to disclose your ongoing sick leave when applying for a new job, either in the application or at the interview. In the long run, however, I think it is good to be honest. Let's say you don't mention anything about your sick leave at the interview and get a job at 100%. If you are still on long-term sick leave at 25%, this information will have to be passed on to the employer, who then has a rehabilitation obligation towards you.
If you have a permanently reduced working capacity, you may be entitled to sickness benefit, read more here: Sickness benefit for permanently reduced work capacity - Försäkringskassan (forsakringskassan.se) External link.
Regarding which jobs you can/should apply for and at what level of employment, I leave it up to you, the doctor on sick leave and the social insurance office to assess.
As a member of Naturvetarna, you can always contact the member advisory service for further help.