In Gmail on my MBP 2012, in Forward email situation, I cannot modify the “Subject” entry. Why not?

While this situation within Gmail forwarding, may appear trivial to some, given that trying to delete unwanted content e.g. from previous emails in the current stream of more than one email on the same subject on either my iPad or iPhone is extremely challenging, and often does not work properly, I need to use my MBP 2012 to be able to easily perform the requisite deletions! Appreciatively, Bruce

>> However, on my MacBook Pro 2012, I cannot do so

What happens when you try to forward a google mail message? Can you show a (redacted) screenshot?

When I try the same (on a slightly newer MBP), I get a popup where I can enter To: Cc: and Bcc: (these 3 are empty). In the Subject: field (showing Fwd: <original mail subject>) I can click on the text and edit it.

Gerwin Jansen: Sounds impressive! What is your MBP model and Mac OS?

 Regrettably,on my MBP 2017, under the latest up to date Max OS, although I can access to CC and BCC fields, Gmail behaves the same way as on my MBP 2012, under Mac OS 10.10.5, I cannot duplicate your successfully executed modifying the Subject field process.

What else can I try?

Hi Bruce, as you're asking this for an older MBP (2012) I tried with on someone's Early MBP (2015, Catalina, 10.15), on that device it is working. I could try a newer Mac but since you already tried on a 2017 model? Makes me think it's something else. Now re-reading your question, you mention "Gmail app" - I didn't realise this but I'm using the Apple mail app for this. Are we using the same mail app?

Some versions of Gmail or apps may have a hidden menu item to change subject. 

https://www.solveyourtech.com/how-to-change-subject-line-in-gmail/

Gerwin Jansen: Thanks. Your reference is for a Reply. Does the same process apply and work for the Forward function, which is my continuing issue.

BTW, I can modify the Subject line for a Forwarded email on each of my iPad Air 2 and my iPhone SE, but the overall challenge is handling the font size, that, when increased, creates challenges with the limited portion displayed on the screens smaller than this on my MBP 2012 & 2017!

I await a response to the applicability to a Forwarded email.

Appreciatively, Bruce

I'm not referring to a Reply?

I tried on macOS devices (2 meanwhile) and I'm able to forward gmail messages using the Apple Mail application and I'm able to change the subject:

Hi again Gerwin Jansen: Nothing I try in my “Forwarding” an email from my Gmail Account permits me to modify the subject content on my MBP 2012, as I can do so successfully on either my iPad or iPhone. I am about to accept that disappointing reality, unless anyone can suggest a likely resolution!

Appreciatively, Bruce

Which email application are you using? I think you didn't mention that, can you post a sample screenshot like the one I posted above? If we use the same application and for me it's working and for you it isn'n then we have a stalemate ;)