Is it possible to download a single sentinel 2A image from the year 2017 to 2020?
You mean of a specific date?
This is possible here: https://scihub.copernicus.eu/
Tutorial: Download Sentinel-2 Imagery (10m resolution) for Free - YouTube
Perhaps @ edmundnokrach asks for an alternative to requesting a frame to be retrieved from Long Term Archive storage (greyed out tiles in scihub).
There are various national mirrors that might have older tiles available.
Sentinel-2 frames are also accessible from Google Cloud container where all tiles are available, from 2014 and on, with the capability to even download singular bands or metadata files: https://console.cloud.google.com/storage/browser/gcp-public-data-sentinel-2/tiles
There’s no map or graphic browser, you need to know each tile’s code and specific date to navigate, but this not a major issue.
Thank you for the responses.