Why did the "delete", "move" and other options stop working in my Yahoo email (even when I rebooted)?

That is a glitch. Try switching to Basic Mail may help if this is happening using full featured mail. It is less loading intensive. Go to Settings under the gear, Viewing email tab and get Basic Mail at the bottom of the next screen.

A security program or web extension may be blocking Yahoo features or they may be other browser-related issues you will need to troubleshoot and fix. Yahoo cannot fix problems related to your web browser or other programs installed on your device. Please follow all the steps in this Yahoo Help article:

Fix problems with Yahoo not working properly

https://help.yahoo.com/kb/mail-for-desktop/fixed-s...