User Issues with Windows 11 - sluggish/slow

Hello!  We are a small company that fully utilizes Office 365.  We recently purchased a Dell 5540 i7 which is our first machine on Windows 11.

Problem: Windows programs including Outlook, Teams and One Drive are running very slowly. Sometimes it lags so badly, the only way to proceed is to reboot the machine, which is impractical to have to do multiple times during a work day.

Our IT is outsourced and they have speculated that the large graphic files we're working with on this machine are causing the slowness, or perhaps Windows 11 isn't as stable as Windows 10.  But we were also told that to transfer this machine from 11 to 10 would take too much time.

Has anyone else had this experience with Windows 11, or detail as to what might be causing this?  I'm not getting confident answers from my team and before we take a drastic step like changing the operating system or replacing the machine, I'd like to understand what could be causing it.