It appears that the only way how to get PowerPoint presentations (.ppt, .pptx) from Keynote iCloud presentations (.key-tef) is to use Keynote and simple use File ► Save/Export function to save key-tef to ppt file. No other software can be of help here, you really cannot convert key-tef to ppt without Keynote.
Convert Apple Keynote iCloud presentation file to Microsoft PowerPoint 97 to 2003 presentation.
We have found one software suitable in our database for this conversion.
Apple macOS / Mac OS X software - convert key-tef to ppt on OS X
The most popular presentation software for Mac
Convert from key-tef file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.