How to use graph api to get columns of item from sharepoint

I have a sharpoint documentLibrary "account". I have custom attribute IsAuthorized bool field.

This document library has a folders "Microsoft", "TCS"

 

I have uploaded 2 files under the folder "Microsoft" & set the IsAuthorized = false and 1 file is added under TCS folder with isAuthorized = true. 

 

Now i want to get those two files with IsAuthorized field from folder name = "Microsoft" using Graph API.

 

 

I am able to fetch the folder and exact 2 items from it with below get query but unable to get custom fields.

 https://graph.microsoft.com/v1.0/sites/manojpatel20dec.sharepoint.com/drives/account/root:/Microsoft:/children

Alternatively I tried: Below query gave me 3 files with fields but did not filter the folder = Microsoft even when i added &filter query string. Filter was ignored.

https://graph.microsoft.com/v1.0/sites/manojpatel20dec.sharepoint.com/lists/account?select=id,lastModifiedDateTime,lastModifiedBy&expand=items(expand=fields(select=IsAuthorized)) 

 

What should be done to get only 2 files and fields in one go using Graph API?