Outlook Running Very Slow and Laggy

Your post doesn't contain enough information to troubleshoot performance issues.

Are we talking about Outlook Classic here?

What do you consider a large mailbox and folders in GB and number of items within the folders having the issue?

Which mail account type are you using? Exchange Online, Exchange On-premises, Outlook.com, IMAP, POP3, other?

If you are using an Exchange account, how do you have your Cache Mode settings configured?
File-> Account Settings-> Account Settings...

When you open Windows Task Manager, do you see a high CPU or Disk usage for the Microsoft Outlook process?

Can you repro the issue in Outlook Safe Mode?
Start-> type; outlook.exe /safe
(note the space in the command above)

Which COM Add-ins do you have installed and activated?
File-> Options-> COM Add-ins

Additionally see; Outlook doesn’t start, crashes or shows Not Responding | Robert 365