Using the word Cannot or Unable in a pip form and ambiguous words

Hello

This might be a bit of a silly post but I am undecided on using the term "Cannot" or should the term "Unable" be more appropriate. The reason why I am asking is the word "Cannot" means to me that you cannot do something full stop but if you are able to do something but with problems then the term "Unable" would be more appropriate. Also being as it is based on activities and functionality then it is also based of ability so the word able or unable would be more appropriate than the word "can" and "cannot".

So for example would it be better to start the activity explination like this:-

I suffer from(with) - (description of disability or mental health problem) - and I cannot do the activity of washing and bathing (for example) safely, in a reasonable time period or to an acceptable standard because..........

Or would the word "Unable" be better? For example:-

I suffer from(with) - (description of disability or mental health problem) - and I am unable do the activity of washing and bathing (for example) safely, in a reasonable time period or to an acceptable standard because..........

The reason why I am asking this is because I am a little concerned about using ambiguous words like "can" or "maybe" or "sometimes" that then would raise the prospects of doing that activity may include better days when infact each day is the same and does not vary.

I might be completely overthinking this but it is just something that I would like to clarify on this forum before we click the submit button on my brothers claim

Thanks for your advice in advance. It is always appreciated.
Kind Regards
Waxwing

Thank you LL26 it has been most helpfull

Kind Regards
Waxwing