How do I keep my emails in date order? I do not want Tbird to rearrange them into conversations!!

Then turn off threading! the instructions have been in the support documents for a number of years now. https://support.mozilla.org/en-US/kb/message-threading-thunderbird#

I will include a picture of the settings that replace the Changing default threading mode from that article so you will know them when you find them

Many Thanks Matt!

I have followed the instructions to turn off threading, but emails are still grouped in conversations. If I change to Grouped by sort, that works grouping them by day, but I don't want any grouping.

When in Unthreaded or Threaded some messages are not even visible in the inbox. It's currently unusable

Did you propagate the settings to all existing folders?