Thanks, well to respond to your questions:
"Could it be you started using a network or cloud drive - they can cause havoc with Audacity."
I have been using a network almost constantly with Audacity, well before these problems started popping up.
"Are you having storage capacity issues - possibly using a compressed drive?"
I am not using a compressed drive and do not have storage issues.
"Did you install Wondershare, Filmora, or Uniconverter in January ?"
I did not install any of those. I have no idea how Wondershare got on there.
So that puts you at going back to review Steve's posts, starting with this one:
steve wrote: ↑Sun Apr 18, 2021 10:47 am
"Are you able to generate a tone? (Generate menu > Tone)
If so, can you play it?"
Yes, I can generate a tone and play it. However, I cannot export the tone or save it.
Any further suggestions?