Outlook running slow? Do these three things first

Check mailbox and OneDrive sync size, disable unused add-ins (File > Options > Add-ins > COM Add-ins > Go), and turn on Cached Exchange Mode with a shorter sync window such as three months, via Account Settings. A bloated PST/OST file is often the real culprit, not your PC.

Coach's tip: if Outlook is still crawling after that, check for a stuck search index rebuild running quietly in the background.