First, you have to create the field under Activity in the Object Manager and assign it to the event layout. Next, in Setup, type Global Actions in the Quick Find box. There, you will see the New Event action. Click Layout next to the New Event action. There, you can add custom fields.
There may be something else going on as well, but to clarify: custom text fields can be indexed but are not indexed by default. You must open a support case to have create the index for that field. I had to do this recently for a reporting reason. I would think it should make search more reliable & faster as well, but I have not had that use case exactly....
You can definitely do this in PROD provided that the custom field(s)/object(s) are not referenced by anything that you can't change directly in PROD:
References in VF pages or other UX components will fail at runtime
If you are in the habit of doing changes in scratch org/sandboxes and then deploying to PROD, then you should stick ...
Those IF are useless. Instead of writing:
you could just use condition, so the whole formula could be rewritten as follow:
NOT( ISBLANK( TEXT( Membership_Source) ) ),
ISPICKVAL( Category, 'C' ),
FLOOR( ( Account.AnnualDate - DATEVALUE( Activation_Date) ) / ( 365 / 12 ) ) >= 12
That's why it ...
You object name should be extracted from Object Name field in your image.
So it should be res__Accs__c and res__Accs__r and not the field label and plural labels.
Both field label and plural labels are generally available when configuring Custom object tabs.
From Setup --> Quick Find --> type packages