Moving your Outlook OST file to another drive can really help if your C: drive is getting full. Outlook doesn't let you simply drag and drop the file, so it's a little hard, but you can do it.
Here's a simple way to do it:

Locate Your OST File: Most of the time, it's at C:\Users\AppData\Local\Microsoft\Outlook.
Choose a New Place: Pick a folder on a different drive that has enough room.
Change the settings in Outlook: The best method to do this is to either make a new Outlook profile or modify the default location in the account settings so that Outlook knows where to look.
Copy and Try: Move or copy the OST file, and then make sure Outlook opens without any problems. Always make a backup first!
You can read this expert tutorial to learn how to do this step by step. https://www.trustvare.com/blog/move-ost-file-to-another-drive/