Yes of course, we have to understand this sentence looking at the context, so there is a clue the possessive adjective"their" which always takes a plural noun, so the second is better to use in this situation.

Amanda is correct. It depends on the context. in the first sentence "Everyone" is treated as a group of people where you may not know who they are. It is more like an uncountable noun. "Everyone alive today either has or had a mother." In the second sentence "Everyone" is treated as a small group of people that can be listed; It is a countable noun. "Jane, Bobby, Frank, Sue, Walter, and Sarah are doing their jobs."

It depends on the context. 'their job' (singular) to refer to their paid employment or generally doing what they're supposed to. Everyone is doing their job from home these days. 'their jobs' (plural) if referring to a list of things to do. For instance, children in a family all have a list of chores they have to do on the weekend. The mother says to one of them, "Why are you sitting around watching TV? Everyone is doing their jobs." I would say the first one is what you would hear/use most often.

Everyone is doing their jobs.

The second one.