Is there any doubt in agreeing with the employer to take the full income (100%) for one year, then return his share (60%) at the end of the year?

The issue involves two matters:

1. The ruling on working for an institution where the worker receives 40% and the owner 60%: This contract is void due to the presence of Jahalah (uncertainty) and Gharar (definition) (excessive risk) in the wage. To rectify it, either the wage must be known, or the transaction must be a legitimate Mudarabah (definition) (profit-sharing partnership). A condition for Mudarabah is that it must be based on cash, although there is an opinion that allows evaluating assets with cash.

2. The ruling on agreeing to take the owner's share (60%) this year, with the understanding that it will be returned to him at the end of the year:

First scenario: The owner gives you his share this year in exchange for you giving him 60% of next year's profit. This is impermissible due to Jahalah (uncertainty).

Second scenario: The owner lends you his share this year, on condition that you repay him the equivalent amount from your profits next year. This is permissible, as it is a goodly loan (Qard Hasan (definition)).