RSU vesting after employment ends and W-8 BEN tax rebate

I have an award of RSUs which vested in March 2023 and need to be included in my 2022-2023 Self Assessment return. The share plan is managed by UBS and have been awarded in USD in New York so are foreign income. I am unclear which section I need to declare this income in as I do not have a P60 or P45 from this former employer for the 2022-2023 tax year (having left employment there in 2020 as a good leaver hence keeping my unvested share award). Also, I have had a W-8 BEN completed and in place throughout my participation in this scheme. Does this mean no tax has been witheld in the US or will I still have witheld tax to reclaim?

Hi

As the payment is from your employer, the income should be shown in the employment section if it is included in your P60.
You would then claim credit for the Tax in the foreign section under 'Employment, self-employment and other income which you paid foreign tax on'.
If it's not included in your P60, please include it on the box on the employment page for 'Tips and other payments not included on your P60'.  
ERSM20193 advises that when RSUs payout at the market value on what is called "dividend equivalents" in either cash or shares, such payments will generally be taxed as earnings in the year they are received.  
Please see ERSM20193 - Employment-related securities and options: what are securities: RSUs and dividend equivalents 

Thank you