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Your LimeSurvey version: 6.4
Own server or LimeSurvey hosting: Own Server
Survey theme/template: Fruity
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So not sure if this a actually a bug now, or was a bug in 3.*  but it was something we used a lot and miss it.
Previous Version allowed us to have Q1 = List  and Q2 = Multiple Choice - Same content and Q Codes in both.   Then use the Array Filter / Exclusion to remove the selected answer from the Q2 Multi Select List.

Useful for Questions like:
Q1.   Which of the following is your favourite
Q2.    And which others do you like...

I know that I am able to use Relevance but I have a list with 30 options - so thats 30 entries - and array filter is 1 entry.

I Know the Tip says enter the code of a previous Multiple Choice hence why i'm thinking that this is a feature not a bug, but it did use to work in V3.*

What does the community think?

I don't think a list question was available to be used as a filter in 3.x.

- manual.limesurvey.org/Question_type_-_Mu...ay_filter_exclude.29

This is why Joffm's workaround with hidden multiple-choice and equation questions is so popular.