I am not able to click on a web element in salesforce lightning application

Now try this:

// Wait upto 10 seconds for a_Accounts to be visible... 
WebUI.waitForElementVisible(findTestObject('Object Repository/Page_Home Salesforce/a_Accounts'), 10)

WebUI.delay(2)

WebUI.executeJavaScript('''
document.querySelector('a[href="/lightning/o/Account/home"] > span').click()
''', null)

If that works, you can try removing WebUI.delay(2).