What can reduce the cognitive abilities in a common workplace? There are many types of work that mainly create benefit by thinking, often called desk jobs.

The output is based on the cognitive abilities of the person.
It typically happens in an environment we call office.

A working person has some amount of cognitive abilities. They are certainly multidimensional, but that has no relevance here.

There are things that can reduce these abilities. Some of them are obvious, but it would be interesting to know all that are important for a common desk job. I assume there are not so many of them that this becomes a list question. Many of them are obvious, but I assume there are others.

Obvious are for example:


Tiredness
External distraction by unrelated activities of others


Some points or classes where it is not obvious are:


Maybe some types of mental illness? Major depression seems likely?
Possibly external physical influences like freezing?


There are certainly unusual points applying only to few people, for example a person extremely distracted by harsh light. These are interesting, of course, but I mainly think of common things.
One of the most significant factors impairing cognitive abilities in a typical office environment is the noise. It is well-known that quiet environment is essential for good concentration. For instance, WHO recommends school classrooms should have noise level as low as 35 dB during classes. Yet a typical office environment can be as loud as 70 dB, which is about 30-50 times louder.

There are loads of articles describing the effects of different levels of noise on various cognitive abilities, which inevitably show that noise above 60-65 dB has a significant impact on mental activity, and noise above 75 dB has a lasting effect which can be measured 4 hours after the exposure. For reference, most public transport is louder than that, and a subway can be as loud as 95 dB.

It is well known that private offices (which reduce the noise quite a bit) can boost productivity significantly. Unfortunately, they are too pricey, or at least are seen as such, to become widespread.