Fields Missing from Flow, but Available in Process Builder

Question

I'm logged in as a System Admin (who has permissions to everything, from what I can tell). When I create a workflow in the Process Builder, I'm able to access all fields, as intended (in the example below, I'll be referencing the SH_Overseeing_Tech_Contact__c in the Opportunity object). However, when I go to create a flow in the Flow builder, I am unable to access this same field.

Here is an image from the Process Builder, showing the field I'm attempting to access. This first shows a saved Process, with the field selected. The second image shows a new process, and being able to access the field:

I've read in a few places, sometimes the Flow will not show a custom field in the dropdown list, and it will have to be searched for by typing in the field name. In this instance, the field did not appear in the dropdown, nor when searched for directly. Here are some images from the Flow, showing the attempt to access the same field, with no results:

If there's a certain permission I'm missing, can someone let me know what that might be, directly? I find it odd that the Process Builder can access all fields, but they're not available from Flows.

Here is the particular field in question's field-level-security options. As you can see, it's 'visible' to each profile:

Answer 1

Your last screenshot clarified it - the field you're looking for is a long text area field type and your screenshot is related to the criteria of a record-triggered flow.

Long-text area fields seem to not be supported to filter by in criteria of a record-triggered flow. I haven't found official documentation for it (though it's mentioned here), but it's easy to see it's being excluded by doing the following:

• See your custom long text area field does not show up in criteria of a record triggered flow
• In the same flow, the field is accessible from an assignment, decision, or update element.

It's a known limitation that you can't filter by long text area in SOQL so you'll notice those field types missing in the Get Record criteria as well.

Not being shown the field seems to be by design.

In your record-triggered flow, however, you could make the entry criteria be met (no criteria or only filter on other accessible fields) and then use a Decision component which can reference a long text area field and be used to split logic from that point on.