"net regular contributions made and distributions taken prior to 2020" for a 1099R for 25 yr old Roth IRA. Made sporadic depos. (<age 60) and wthdrwls (>age 60)?

[grammacn]

1099R for withdrawal from Roth IRA prompts a request for net contributions and withdrawals made prior to 2020. We do not have 25 years of statements to answer this and for a $5k withdrawal getting bank and brokerage to find them would be impractical.
How should we enter.

[dmertz]

Presumably you made your first Roth IRA contribution for some year prior to 2016.  Because you were age 59½ or over in 2020 when you received the distribution (code T or Q in box 7 of the Form 1099-R), the distribution is a qualified distribution.  Since it is a qualified distribution, you do not need to enter your basis in Roth IRA contributions or conversions.  No reporting on Form 8606 is required.