Thanks for the help and pointers
I got it some how, but its by no means straight forward. Therefore a little help, if someone wants to try it.
See picture:
you find the file type settings it in "Settings" Menu Sub menu "FileTypes" (Window left side middle "File Types") press "Add" to add a new FileType
The window under it opens press "Edit Class..."
The window lower right side opens to edit the file properties
(sometimes this window opens automatically)
Put in the name "LibreOffice calc" ID ODS (I'm not sure for what this is) and very important Pri to 5 (or something higher than the prio of Icaros, archive, which is the default)
Press the "Add" in this window to add a file property choose "Match Name" and enter "*.ods" into the field next to it, do not forget to press enter
Press "use" to apply that
now the name is already shown next to the file if you reload the directory
go back to the window on the left lower, press "Double-click" to edit the action of double click
the window in the middle lower section opens to edit actions
press Add to add an action
Choose "AmigaDOS" (where is "Command" as default) and put the program to the field next to it, and a "{f}" behind it as parameter, this is important! It is used as a placeholder for your file when starting the program, if you forget it, it will start the program but not load the file (do not forget to press enter in the field to apply it, its applied when its shown the upper list, as in the picture)
Again press "Use" to apply that
Press use in the lower left window and save in the main file types window.
Now if you double click your Calc file (upper left window the files, as you can see I added the Excel file as well, the third file I' not sure which program that belongs to, never saw before)
it shows the contents in the viewer. (upper right window, Leu open by double click)
hurray!
