以后 = in the future, next time 然后 = and then, after that

以后：Used in time, the future time 然后：Go on to do the action, or say

well, both are time related adverbs, 以后 mostly used in the tail of an sentence，【他走了以后，sth happend】（sth happend after he left). 然后 mostly used in the head of an sentence，[sth happend,然后他走了]([sth happend,then he left)。 but i think the most difference is that 然后 could use independantly as a sentence while 以后 could not。 example: sth happend，然后，he left。（notice the two comma beside 然后） but we never use 以后 in this way,(but we could use 从今以后，it means from now on)

“以后”用来表示时间for time “然后”更多表示动作for action

hi ,first ,their properties are different ,“然后”is like "and "or "afterward" ,which is a conjuction ,but "以后" means "later ",which is an adv. Hope you like it !Good day !