TXB0104: TXB0104 vs TXB0304

Hello Kai,
These devices are different in many regards:

(All references below to the datasheets)
In section 5, the packages/pinouts available are different (although some are the same).

Table 6.2 lists different ESD ratings.

Table 6.3 lists multiple different recommended operating conditions.

Table 6.4 lists different thermal specifications.

Table 6.5 lists different electrical characteristics.

I could continue on, but I think you get the idea. These devices are quite different.