32bits/16bits button grey in 0.99.4 windows7

I recently downloaded 0.99.4 on windows7
I would lke to use it with 16 bits due to a lack of available memory but the switcher button appears grey and is not functional…
Any idea?

many thanks to all

Please, first download last version of Siril.
If the button is not functional it is because no image are loaded. Then, it is not the right thing to do. Go to preferences, and misc.

do you mean 0.99.4 is NOT the last version ?

Yes I do