Can anyone be saved after the Rapture?
Yes, there will be a great multitude of people saved during the Tribulation, according to Revelation 7:14. Now, in my judgment, no one who has heard the Gospel and refused it in this age has any reason to hope they will be saved after they have entered the Tribulation.
Second Thessalonians 2:11 says clearly that unbelievers in the Tribulation will be sent strong delusion. I understand this to mean that the person who refuses the Gospel in this age will be subject to this delusion.
But, there is no question that a great many people will be saved during the Tribulation, and they will pay for their faith with their lives (Rev. 7:4-9).