If I understand correctly, you’re currently not an employee but an independent contractor for this company ? (Not a contract hire?)
You’ve started your own business in a totally unrelated field?
Regardless of the specifics, I will tell you my first knee-jerk in an organization is to worry about how that will impact the persons time/performance. Personally, I have a policy of supporting employees, even at times where it may not instantly help the organization. (I e, I knew an employee would be departing but still made sure we paid for a training program that was relevant to their existing and new role…)
The answer of what to share in this case sounds like it entirely hinges upon the institutional ethos, and your interpersonal relationships there.
By not sharing, and they find out, will that cause bridges to be burned?
Conversely, by sharing, will you burn bridges?
If you’re planning to ween yourself off of your day job, what does that look like, and how will you communicate that?