about to retire but not retired yet, employed but not working any more

I favor pre-retirement Merriam

of, relating to, or occurring in a time before retirement

As in: OED

1990 Intercity Apr. 27/1 Increasingly firms have come to realize the need for pre-retirement courses to help plan the available time.

To retire, one must make some plans - take some steps. This stage include ones finances, habitation, health and other life's needs . The root word retire is retirer, "to withdraw."

A job that requires little or no work yet which still produces income is called a sinecure:

[Merriam-Webster]
1 : an office or position that requires little or no work and that usually provides an income

In the context of somebody about to retire, and who's been relieved of responsibilities, you could say something like the following:

Pending their retirement, their employment had turned into a sinecure.