Cai Lun of the Eastern Han Dynasty invented paper in the 1st century AD, but paper was not popular at that time.
For example, during the Three Kingdoms period in the 3rd century AD, Guan Yu read the Spring and Autumn Period under the moonlight, reading bamboo slips. During the reign of Emperor Xian of the Han Dynasty, the "Edict on Clothes and Belts" was written in blood to Dong Cheng. It was a silk script, written on cloth. Because there was no paper at that time.
It was not until the Jin Dynasty in the 4th century that paper became widely available. That’s why calligraphers like Wang Xizhi appeared, and “running script” also appeared. Before that, it was all seal script from the Qin Dynasty, official script from the Han Dynasty, and Wei stele from the Three Kingdoms period. Before that, all were bamboo slips and knife-engraved scripts. Cursive writing may occur.
Until the Tang Dynasty in the 6th century, official documents and classics were still written on bamboo slips. Although "paper" appeared in large quantities in the Tang Dynasty. But the paper at that time was rough and of poor quality. Only Buddhist scriptures were written on the paper, or some calligraphy characters written by literati were written on the paper (not too important). Formal documents and historical books are still bamboo slips. Therefore, in the TV series, when people in the Tang Dynasty studied, they still read bamboo slips.
However, during the Tang Dynasty, papermaking spread to Korea, Japan, Central Asia, and Europe. Europeans also had their own paper at the earliest, including ancient Egyptian papyrus and parchment. The papermaking technology of the Tang Dynasty gave Europeans new inspiration. Papermaking could use cheap and easily available plant fibers, which also led to new developments in European papermaking technology.