I am trying to add some validations between two columns of a list [Start Date] and [End Date] with the formula below

=[Start Date] < [End Date]

however this produces

So I triedto test with the same column as below and it saved successfully( although this is not useful as a formula )

=[Start Date] > [Start Date]

This gets more confusing because some videos on the net show that this is possible however on my Office365 account I do not see theInsert Column: part in my column settings

Source: https://www.youtube.com/watch?v=zm5vnSNESPI

Do you have an idea what am I doing wrong? I tried this both on Office 365 and our on premisses SharePoint and both have the same issue. If this is happened after some upgrades of SharePoint how does one achieve such cross column validations now-a-days? Thanks