Do I tell the truth when I resign?

[malificent7]

I do like where I currently work but have secured an amazing opportunity elsewhere.
Part of the reason why I have taken the opportunity outside is that I feel pigeon holed here and will therefore not be afforded the opportunity to progress. Do I mention it?
I do want to leave on good terms so I would be polite.

Depends on if you get an exit interview and what they ask.

Why haven't you said anything about it before?

Just express it positively - you’ve appreciated ABC about your current job, but the new gig offers you XYZ and that’s why you’ve taken it, if you feel the need to explain

Honestly, don't bother.

Stick with:
New job was too good to turn down, Thanks for the memories...

This is a good approach

This

I like this. You could say you feel that the new job will give you more opportunity for progression, which is saying the old one won't, without actually saying anything negative. It might be good for them to hear that that's why they lost you.

Why bother? It won't change anything for you. Just tell them it's a great opportunity blah blah blah and be done with it

Yes this. I'm sure they'll (or should) read between the lines. 🌹