Audacity 1.2.6 and all later versions have simple (linear) Fade In / Fade Out effects in the main part of the Effect menu.
Audacity 1.3.x and 2.0 has effects called “Cross-Fade In” and “Cross-Fade Out”. I don’t remember if these were available in Audacity 1.2.6 (I’ve not used that version for a long time). These effects are not really “cross-fade” effect (they don’t cross-fade anything), they just provide an alternative fade shape. The easiest way to “see” what these effects do are to apply them to a generated tone, then you can literally “see” the shape (it’s actually the square of a linear fade). You will find these effects below the dividing line in the Effect menu list.
There’s a list of fade plug-ins here: https://forum.audacityteam.org/t/fade-plug-ins/19596/1
Note that these may not be complete - the most recent versions are usually available from the first post of a topic.