You can't import UA data into GA4 unfortunately. This video shows you how to save historic Google Analytics data (pre-2023) down to google sheets so you can look back at it.
Using Google Sheets has limitation that only reports are exported. It means you need to know all reports you will need later. Seems like painful process. Is there free way to export all UA data at once and create reports on demand later?
Unfortunately not. There are a few paid solutions that can import everything into BigQuery and recreate in a GA style dashboard (eg www.databloo.com/universal-analytics-backup/). But it needs some justification on how much you'll need to access it in that depth in future.
I'm hosting a webinar on this topic on May 30th 2024. To join, please register at www.linkedin.com/events/ga4essentialsforecommerce7196808885930786817/
Correct Dylan - with this tool it exports the data directly into Google Sheets, and once that's done, you've got the data forever. The important thing is to make sure you do it before 1 July.