my trash icon didsappeared when deleting many e-mails

Hi, welcome to the Apple Users Community.

I am going to assume the icon has gone missing from your taskbar at the top of the Mail window.

If you click the View menu, near the bottom of the menu list is Customize Toolbar which will bring up a window where you can drag and drop the icon bag onto the tool bar.

Best of luck

Safe Boot, (holding Shift key down at startup), does the problem occur in Safe Mode?

Safe mode attempts to repair Disks & clears lots of caches & loads safe Drivers, & prevents loading of 3rd party extensions, so if Safe Mode works try again in regular boot.