A possible reason for scuttling Type XXIII submarines first

Why were Type XXIII submarines among the first boats scuttled during Operation Deadlight?

Possibly to prevent Soviet access to capable coastal submarines whose importance is often overshadowed by the larger Type XXI.

Preventing Soviet access is the suggested explanation for giving the Type XXIII boats early priority in Operation Deadlight. The ocean-going Type XXI attracts more attention, but the smaller coastal boats were considered particularly capable and potentially worrying in their own role. This is a speculative explanation of the disposal order, with no documentary decision cited in the answer.