I actually found myself in a very similar situation and created a side hustle that did not conflict with my position. It is in a completely different space and provides me (after 20 months) a substantial income over and above my salary from my current job. I'm so fortunate to have a solid, nicely compensated job that provides great benefits, perks and security that I can easily handle in 4 hours a day. My manager is super happy with my work, gave me a bonus at year end and let's me run my own show. I love that I have plenty of time to devote to my side gig and I Loovvveee all the extra income and creativity it provides. I'm not alone in creating my side gig. I have several friends that are doing the same thing. We created projects that light us up, speak to our passions and each of us is preparing to make our side gigs are primary jobs eventually. Right now we are secure with our boring but lucrative and stable jobs that allow to grow our businesses. We are available 24/7 to our companies but are never really needed beyond 4 to 5 hours a day. That leaves us available to our passion projects and they are growing.

Maybe it's not fast paced enough for you. Weigh your options at this given point in time to see whether job seeking or waiting out the 18 months is a better for you. Remember, the grass isn't always greener and there's a possibility taking on the next role at your current place of employment might be the challenge that you need. Until then, keep networking within your organization and making the best of the situation.

18 months is a general policy - and every policy has an exception. I was in jobs less than a year and was moved to new jobs People said it could not happen, but it did. 6 months into a role I contracted at, I was hired full time, 1 year later another move and after a few years was asked to move to another job, which I gladly did, then 8 months later was hired into another role I held for 8 years, Never say never. I would look and if you are strongly interested and qualified for an opening, inquire - it also lets others know that you are interesting to do more and could be the opening you need.

This is purely anecdotal, but I had a very similar experience in a company and I left. Life is too short to be that miserable. I had discussed my boredom and my general situation multiple times (both formally and informally) with my supervisor, as well as on one or two occasions with the department manager, and got nowhere; in fact, I was told multiple times that I needed to give it time to settle into the role (the fact that I was crushing it, as you seem to be, was irrelevant), and the company had the same 18-month policy. I was mostly blocked from taking on any kind of stretch project or anything above and beyond my description (which it sounds like you might not be). I ended up going above the manager's head after being stonewalled so often to negotiate my departure. He was not best pleased, to say the least, and I wish that situation had been less contentious, but I honestly felt and feel that I had tried to communicate the issue before then and gotten nowhere. There were some additional circumstances surrounding the initial job description, etc., that made the choice easier for me, but bottom line -- getting out of an organization that would intentionally hobble me like that, even after I had communicated it to them and proposed multiple alternative solutions, was definitely the right choice. Start looking around.

Is the minimum 18 month waiting period an official company policy? If not, then start applying for new jobs that fit your skills and interests better. If it is company policy, look elsewhere. No reason to be bored and frustrated hoping that in 6 months you might be able to transfer internally. Sounds like the job you have isn't a good match for you, so see what else is available.