can you explain what happened?

hi there, I have been using the electro template version 2.x.x for a long time, then there was an update to 3.x.x but after the template was updated there were many errors even though I was using the same data. What is it?
electro v.2.x.x https://texco.co.id
electro v.3.x.x https://dev3.laysandermediatechnology.com