It is possible, but award availability on this route is often only in Economy. If you want a premium cabin award, you're more likely to find seats booking around 1-2 weeks out.
When searching for redemption seats on the Singapore Airlines website, you need to select "Show flights for Star Alliance" on the search results page to view Lufthansa availability. Otherwise it just shows SQ flights by default.
This is currently available in First, for example:
I haven't ever seen availability other than SQ but its because I am looking at flights from Australia - I wish it would show options of a Aus leg with SQ and star alliance for other leg
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