If you have access to the email account(s) you've used for the past 8 years, and have not deleted all your ticket purchase confirmations etc, then at least those tickets that you purchased yourself and mailed to you can be retrieved from your email.

(EDIT: searching for boarding passes might be a better strategy - if you habitually have them emailed to yourself upon checking in - because many of your flight bookings in the 2020-21 timeframe were probably unilaterally cancelled by the airline due to the pandemic - so boarding passes are a more likely indicator of flights that you actually took, rather than purchase confirmations)

Your Flying Blue history will only show you the last 3 years' worth of transactions.