German life insurance policy payout - what is the "gain"? How to calculate the years?

I have had a payout under a German life insurance policy which I took out in September or October 1992 whilst living in Germany before becoming tax resident in the UK in 1996. This policy paid out after 30 years and just paid two amounts: the insured sum and another amount comprising a "share in surplus including share in valuation reserves and final surplus share". No tax was withheld in Germany. Is this combined amount of "share in surplus including share in valuation reserves and final surplus" the "gain" I need to report in the Foreign Income section? I do not understand the "optional" section about the years taken out. The so-called "help sheets" are utterly confusing. Please advise.

Hi
Please refer to guidance at:
HS321 Gains on foreign life insurance policies (2023)
Thankyou.