Configure the option "Underline 'old' German spelling in blue" (Tools > Options)

Here you can configure if Presentations marks with a blue underline those words that do not follow the current German spelling.

Supported on: At least Windows Vista
Registry HiveHKEY_LOCAL_MACHINE or HKEY_CURRENT_USER
Registry PathSOFTWARE\Policies\SoftMaker\Presentations 2016
Value NameDiffCorrections
Value TypeREG_DWORD
Enabled Value1
Disabled Value0

softmaker.admx

Administrative Templates (Computers)

Administrative Templates (Users)