Mail: export mail data

tried to export calendar data to a preferrably .csv or a .ics or other file. This can be performed by most calendar clients, so it is a must for nextcloud. Could only find work of users writing code which I cannout use because I am using a β€˜snap’ installation on linux.
Should be an easy task for nextcloud devs to create a button asking for a time range and then exporting the data in any readable ASCII or UTF-8 format, maybe as a plugin.
β€” this is a key-feature of all good programs β€”
but maybe nextcloud wants to choose a proprietary direction to compete with MS* or GOO (goo!) ;c( .