It’s perhaps key for investment in bank? (5,6)
I believe the answer is:
legal tender
'bank?' is the definition.
The definition and answer can be both related to property as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'it's perhaps key for investment in' is the wordplay.
'it's perhaps' becomes 'eg' (for example).
'key' becomes 'alt' (the Alt keyboard button).
'for investment' becomes 'lender' (I can't justify this - if you can you should give a lot more credence to this answer).
'in' is an insertion indicator.
'eg'+'alt'='egalt'
'egalt' going within 'lender' is 'LEGAL TENDER'.
(Other definitions for legal tender that I've seen before include "Valid currency" , "Useable money" , "Notes, perhaps" , "Official currency" , "... [HALF CROWNS] no longer this" .)