iMac Catalina: File Sharing and Calendar issues

I have an ancient iMac which I have used as a backup for my laptop and also when a large screen makes the task easier. For some years I had it running OS Mojave very successfully as I was using an old version of Adobe InDesign which does not run on a 64 bit system. I recently decided to abandon Adobe and update the iMac to Catalina. I did this by downloading the OS Catalina combo update from Apple. It went well and the iMac has a new lease of life. There are, however, 2 problems:

1. The system refuses to switch on File Sharing. It allows Printer Sharing but not File Sharing. Given the primary use of the iMac is as a backup, this renders it virtually useless.
2. The other problem is a bit more bizarre: The Calendar app works fine but only displays an Islamic calendar which shows that today is 3 Bahman 1404. I have tried to fix the problem in the Preferences but that allows me to display only Chinese, Hebrew of Islamic calendars, no Gregorian. Toggling the Islamic calendar has no effect on the problem.

I've attached screenshots of both problems and any advice would be gratefully received.