Working or not working shouldn’t make any difference to your PIP application or acceptance.
If anything, if you work at a large Co with access to OH resources, reports from OH which draw attention to your difficulties, work-arounds, aids & adaptations could actually contribute positively to your case. The assessors aren’t just reading what you’ve written on your form, they will be looking for reputable proof sources like Doctors, Consultants and yes, employers.
I would suggest you don’t quit work but allow your employer to terminate your contract if you are unable to continue working .
Has your employer provided all reasonable adjustments to help you continue to work ?
Have you had an assessment from Occupational Health ?
Depending on what job you do could you reduce your hours or work from home ?
It’s such a massive step to take and I don’t know how old you are ?
I’m very lucky as I have Income protection as an employee benefit so I’m not working but technically I’m still employed and paying tax and national insurance and I’m in my early 60s.
I had to have an assessment and provided medical evidence from my Neurologist, GP , MS nurse , physio etc to my employers insurers.
My sister who also has MS was medically retired from the NHS in her late 50s after an assessment by Occupational Health and medical evidence.
I note you’ve applied for PIP so you will already have gathered medical evidence which is good.
Only you know how you feel and if it is really the best thing for you to finish work I hope you have plenty of support from all those around you.