No, you cannot use your SoFi rewards points if you book directly on Expedia.
Your Expedia account and your SoFi account are separate entities with their own login credentials and rewards systems. To redeem your SoFi rewards points, you must book through the SoFi Travel portal.
To access the SoFi Travel portal, sign in to SoFi (on the app or website) and select your profile > Our products > Member Benefits > Travel.
Please note, you will not earn Expedia rewards when you book through SoFi Travel.