On https://quelea-projection.github.io/docs/Planning_Center_Online (docs/Planning_Center_Online) the text says you have to setup a download path for additional files and links you to https://quelea-projection.github.io/docs/Import_Export (docs/Import_Export).
Testing with 2021.0, in the options UI, the Import / Export section (Tools > Options > Import/Export) only mentions Elevanto and offers the user the ability to input a client ID.
It would appear the documentation needs updating, which I'm happy to do, but I'm unclear where to specify the Planning Center Online download path at this stage. It appears you can import from Planning Center Online still (at least it's in the menu), so I'm wondering if the option has just been moved.