Basically when 4E happened there was a 100 year time jump and an entire continent appeared on Toril introducing dragonborn while magic went crazy some mountains spontaneously started to levitate, etc.
But 4E was a gigantic failure and in their panic they reset the FR in 5E. They did not undo the time jump, but the extra continent vanished again and everything that was ever popular in D&D was brought back. The old characters from the Drizzt books were reincarnated because reasons, the old gods like Bhaal were resurrected, etc.
