Products can appear greyed out on the stock tab of the stock takes for the following reasons:
Auto Consumption
Products set to be auto consumed will be greyed out, this can be managed here:
Click the Admin Cogs
icon along the top tool bar.
Click Advanced Stock, then Outlets and Stores.
Edit the outlet that controls the stock take, then click the Products tabs.
Click the Configure heading Auto Consumption.
Locate the product and use the drop down box in the Consumption Method column to adjust settings.
Scroll to the bottom and click Save Settings.
Stock Items
Products linked to a stock item will appear greyed out, to manage products linked to stock items:
Click the Admin Cogs
Click Products And Categories, then Stock Items.
Locate the stock item, then click the Edit icon.
Click the Linked Products tab, then add or remove the products as required.