Post Clean install, user setup says still managed by company

The company has to remove their control of the computer. They should have done so when they gave the computer to your friend.

MDM overview for Apple devices - Apple Support

There is no way around it – that's one of the reasons companies use MDM. Well, technically Apple can remove MDM but you'd need to conclusively demonstrate proof of ownership of the Mac, i.e. a sales or donation receipt with the serial number of the machine, and since you 'got it from a friend' I rather doubt you have one of those.

Are you certain it was his to give you? Generally, company IT policies require return of equipment, or if the entire company was dissolved then the computer is a physical asset that would become part of the liquidation. If they gave it to him to keep, they should have removed it from their MDM first. If it's on their MDM, the company can remotely access your computer and that could present a big risk for you. Ask your friend to ask the company to remove it from MDM.