I see that the Mail application on your iPhone X unexpectedly quits when you try to delete multiple emails. I'm happy to help.
Force an app to close on your iPhone, iPad, or iPod touch -- First, force close the Mail application if it's open, then -- Restart your iPhone, iPad, or iPod touch -- Once it's returned to the Home screen, test the issue.
How to check the storage on your iPhone, iPad, and iPod touch -- If restarting your iPhone didn't resolve the issue, you can offload the Mail application, then reinstall it again. Go to Settings > General > iPhone Storage, scroll to the Mail application and tap "Offload App". Once the application has been removed, reinstall it again and test.
Let me know how that goes.