Hello Åke, welcome to the forum!
First of all, when you have a question for the forum you should start a new topic with a subject line that describes the issue, NOT reply to the “sticky” introduction post. I have moved your post to a separate topic.
The 35J and 35OE payware models are intended for Prepar3D V4/5 but are compatible with FSX, with the exception of some functions that are not supported in FSX. There is no separate FSX model. This is described on the product page and in the documentation.
None of the Bookmark Draken models are intended for MSFS2020 and they have not been tested on that platform, so I cannot help you with any problems you have with any conversion tools etc.
Thomas Nilsson, Bookmark Simulations