Please recommend a fantasy novel with a transmigration theme.

When he was about four or five years old, he once read a fantasy novel. It started with a college student (or a high school student, but he was still a student) who was suddenly transported to a mysterious place while using a computer. It was like a prairie, boundless. He thought about it and found that he could use fireballs to kill some rabbits. He also found that he could get a crystal after killing them, so he picked them up and kept them. As they continued to kill, they finally reached the edge of the grassland. There seemed to be a barrier blocking them, making it quite difficult to get out. However, the protagonist adjusted himself and finally broke through the barrier. Then, he saw a beautiful woman floating over. She was a jungler. Of course, the main character would call her a fairy. It turned out that the beauty was here to collect the crystals dropped by the monsters. It just so happened that the main character would take out a handful. The beauty was naturally shocked. They were all good stuff. Then, he left with the beauty. On the way, he found out that the grassland was quite extraordinary. The people here would only organize a group of people to break into the barrier and collect high-grade crystal stones after a long time. Moreover, they did not dare to go too far. After that, he seemed to have gotten to know a few beautiful women and even became friends with Wind Elementals. Of course, his spells were first-class... In the end, he returned to reality. It turned out that Earth was about to be invaded by foreign enemies (the kind of aliens). Some kind of powerful existence sent him to the dream to train, and then he relied on these people to save Earth. It seemed that there were still a few who had fallen asleep together. They had joined forces and fought together, but they had not killed all the aliens. After that, the 1,000-year-old Mummy came, and he had been training for a long time. After that, it was not clear... At that time, he was in his third year of high school, so he didn't read much. He only read the beginning and listened to his classmates talk about it later. Now, she wanted to read it again, but she had forgotten what book it was. This is my first time reading a fantasy novel. I miss it. I don't know if you know anything. Please tell me. I'm very grateful. The bonus points that you find are definitely certain Looking forward to it again…