The study looked at " the relationship between anti-transgender bills and Google searches". According to Table 1, there were 40 bills (2 of which became laws).

To determine which were anti-transgender, they used the list compiled by Freedom For All Americans, here: https://freedomforallamericans.org/legislative-tracker/anti-transgender-legislation/

Edit:

The bills found on the above site were cross checked with the ACLU's tracker

The whole process is described under the heading "Context of current study"

There were 40 bills. It's annoying that they didn't include a list of the bills.