I know there was hype for awhile around “transferable skills” and switching careers, but I’ve found this difficult to do even when the job is very adjacent to my current work. I’m wondering if this is happening less these days?

Sometimes it comes down to available number of job and also consider your branding. Updating your resume is one thing, your LI profile and if needed list a few classes geared to what you want to get into. Some volunteer work or simply having an online portfolio if appropriate. Networking helps. Look at profiles of people in the career and pay attention to keywords and terminology used. Look at the job openings and use that terminology as well. Repost a blog in the field and tag the career. Brand yourself for the career. Join and follow online groups for the new career. This not only shows your interest but your passion as well.

Still valid, you have to practice to successfully be able to attach those to the specific needs of the role you're seeking, this comes from practice with research and examples of what it would look like in their role.