Reducing adjusted net income after leaving employment

Hi, I recently signed a settlement agreement with my employer. The settlement figure meant my total pay in employment for 2023-2024 was £128k. This has had consequences on both my childcare account and personal tax. I expect to take a break from working until at least April 2024. I have a few questions: 1. £30000 of the settlement was "tax free". Can this amount be deducted from total pay as part of net adjusted income via self assessment? It doesnt show on my P45 so I am not sure how it impacts my personal allowance. 2. If I make an additional payment into my pension prior to the end of the financial year can this be used to bring down my net adjusted income? If so how long will it take for my tax position to be clarified? I assume I will need to register for self assessment? Thank you for any comments - This has been a distressing time and although the figures I note here are high I am not normally a +£100k earner so all new territory.

Hi PFT1
I'm really sorry to hear that this has been a distressing time for you - if we can offer you any additional support, please just contact us by webchat or phone via Income Tax: general enquiries  As the £30,000 does not show on your P45, it will already have been deducted from your total income, and should not impact on your personal allowance.  Additional personal pension payments will reduce your net adjusted income - if these payments are made through your employer, the reduction will show on your payslip. Tax relief on additional private pension payments can be claimed by contacting us by phone or post via Income Tax: general enquiries, or by declaring them on your Self Assessment return if you complete one.
Thank you.