Google announced the sunsetting of Universal Analytics and ultimately the transition to Google Analytics 4 (GA4).
There will be no future development on Universal Analytics with focus solely on Google Analytics 4 capabilities.
If you want to build up at least a year of historical data in GA4 before the hard cutover, then you have until July 1st 2022 to set up GA4. This will allow GA4 users to make year on year comparisons.
There are gradual steps to fully migrate over to GA4 however, the sooner the basics are setup (creating a GA4 property, platform linking etc.) the better.
Key Dates
July 1st 2022
Basic GA4 needs to be setup to report Year-on-Year data
July 1st 2023
UA will stop collecting data for free GA customers
October 1st 2023
UA will stop collecting data for GA360 customers
+ 6 months
Customers will be able to access their data for ~6 months after UA is depreciated
It is important to note that the major difference and upgrade with GA4 is the new event data model / data collection method. This is a huge upgrade and allows much more flexibility and scalability. Familiarise yourself with events + parameters. Everything in GA4 references an event and uses the same data model that is in place for tracking apps.
https://blog.google/products/marketingplatform/analytics/prepare-for-future-with-google-analytics-4/