The main inventory table can grow to be very large, especially when there are multiple Sales Channels connected.
Each marketplace gets its own Stock and Price column. This will cause your Inventory table to be too large to fit on any screen.
To hide unnecessary columns click on the Columns button:
A pop-up will appear where you can disable various columns by unmarking them and check-marking the ones you want to see in your Inventory table. Once you're done making the changes, click on Save: