BESIDES digital marketing, content creation, copywriting, video production and social media management.
An example of what I believe to be "fun" B2B would be handling end to end for corporate events like showrooms, pop up stores and product launches.
That's such a personal decision, only you can answer it. There are corporate event planners, but many companies will expect you to have a certification. If you have no agency experience, you may want to go work for someone else and get exposure to the many ways clients are served. While you may not intend to stay, you will at least learn how relationships are established, how to set customer expectations, and what is logistically possible for one person to do as a business on their own.