They are going to be more similar than different really. Both lean heavily on the B part of the name (applied Behavioral analysis, and cognitive Behavioral therapy), and at their core are learning new skills or behaviors that more effectively navigate the world (one not inherently designed around an autistic experience of the world(as if there was just one)). They are both about making behavior changes that lead to being more comfortable long term, and that usually revolves around practicing behaviors (often pretty frequently, which can be uncomfortable short term).

I’ll add on as someone that works with trans folks preparing for hormones/surgery, FFS is usually less common compared to other procedures, and is itself a cluster of surgeries that people may choose to do any combination of. Some of those surgeries are less drastic some are pretty intense (graphic warning: basically peeling back a portion of your face from your skull, changing bone and slapping that face back on). The more intense options are understandably not for everyone. FFS (and most other surgeries) usually comes into play after people give hormones a few years to do their thing and see where things end up. Let the canvas stabilize before working on it.