Cross-platform, if federally installed (6)

I believe the answer is:

miffed

I'm a little stuck... Click here to teach me more about this clue!

'installed' is the definition.
The answer and definition are not the same part of speech. However, past participle verbs and adjectives sometimes mean the same thing.

'cross-platform if federally' is the wordplay.
'MIFFED' is hidden within the letters.
But, I am unsure how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for miffed that I've seen before include "Informally offended, put out" , "Aggrieved" , "Annoyed, hacked off" , "Disgruntled" .)

I've seen this clue in the Sydney Morning Herald.

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