Left a job where I was undervalued, navigated three competing offers, now my manager is making my exit difficult. How do I make the right call?

Background, I came out of Federal campus to run a satellite office of a major university here (one of the oldest in the country) The admin staff? Complete cronyism/nepotism - One race made up the entire staff in an area that’s extremely diverse (I was the only white person in administration for facilities). No one actually had the skills to be employed in those positions but hey, they knew someone so that was good enough! Using the Google suite of tools on a MASSIVE scale instead of ANYTHING else, it was the most painful thing I’ve ever undergone. Using finance software as your CMMS (commercial maintenance management system) this was just insane, the system couldn’t send you an email or text if you had a ticket, I had to manually refresh dashboards for 6 buildings. Installing millions of dollars of HVAC without actually having an engineer sign off. They installed humidifiers in spiralized ducting, which is not completely sealed. Then when all of the runs started to rust out the fix was “just put trash cans under the holes” This was an art/textile archive (thus the humidification) I submitted my recommended changes, instead of taking them seriously my client took it as me making him look bad. And started a crusade to undermine me. My area (the HVAC/Facilities shop) had no heating or cooling through the winter, I was written up for spending the money and getting it fixed for the guys. Then I was fired for missing the deadline on a single ticket, after it took them 90 days to work through the student IT staff to get my access right. (Jokes on them I had already a signed offer in hand) On top of that, they hired me away from a lucrative portfolio knowing they were selling the property in 11 months. This was The George Washington University. The facilities department there is lead by the most incompetent group of chuckle fucks I’ve ever had the displeasure of supporting. Saving money so they can enrich themselves through bonuses. My client drove a 200,000 BMW, wore designer and extreme name brand clothing. I now work in the datacenter space and it’s night and day.