Follow below steps to add the new column on the page:
Add the newly added column in the list view you want to show on the page.
Go to the page where you added web part and click the gear icon on the upper right corner.
Select Edit page.
Edit your List Web Part.
Expand the Selected View and choose the view you want to use(In which you have added newly ...
For the columns in a Content Type eg "Item" Content Type, you could use the code snippet below to get it directly:
using (SPSite site =new SPSite("http://demoaam.contoso2016.com/sites/dev/"))
SPWeb web = site.OpenWeb();
SPList list = web.Lists["TestList"];
foreach (SPListItem item in list.Items)
Ideally, by following the steps you provided it should hide the field from list form.
You can also refer the steps from (If anything is missing): Hiding fields in a SharePoint list.
Note: If your column type is Yes/No then you will not able to hide the field in this way (By design).
Also, if you are using Classic experience then you can hide the fields ...
Per my test in my SharePoint online environment, I hide the column in the content type by following your steps.
Then it can hide the column in the forms in modern experience or classic experience.
To troubleshoot the issue, you could create a new column and hide the new column in the forms to check if the same issue will occur.
And then create a new list ...
Enabling attachments has already been covered. You also asked how to copy attachments to a SharePoint document library. You can accomplish this using Microsoft Flow. There's a tutorial on YouTube here.