Save processing modeler output layers to project folder/relative path?

I am building an algorithm in the processing modeler which takes a csv file as input and creates a number of vector layers as output. I would like to automatically save these layers in the same folder as the project file. As I understand, it should be possible by entering the path “./filename.shp”.

I can set the default save path for each layer in the final “Object Sink Parameter-definition” box in the modeler, but can’t get this to work with a relative path.

When setting absolute path, everything works:
C:/Users/Rasmus/Desktop/testfilQgis/målepunkter.shp

When setting only filename (felt.shp), the filename is added to the modelers default output directory path and saved to this path. When running the model on other computers, it will look for the local directory on my machine.

If I use a relative path (./koter.shp) that whole path will be added to the default output directory path (and break since the . folder doesn’t exist).

Only the one folder up path seems to be accepted, but returns a “Failed to create: Permission denied”.

See below image for the suggested save paths based on these inputs:

I’ve looked into using the project_folder as suggested here, but the “object sink parameter-definition” box only takes a path, so I’m not sure how to do that.

And setting the save path manually for each layer every time seems like defying the purpose of building a model. Surely, it must be possible to suggest a relative save path?

project > properties > save paths is set to relative (default).

Thanks in advance!