Both DxO PhotoLab and ON1 Photo RAW create proprietary sidecar files (.dop & .on1) when processing images. But PM+ treats them differently, at least in the Mac version.
1. Process an ORF raw file in DxO PhotoLab and export a JPG. From the PM+ contact sheet, select that JPG and via File->Upload send to social media — Flickr, SmugMug, etc. The image file is selected (and the .dop sidecar ignored) and sent to social media without error.
2. Copy the same DxO-produced JPG to another folder via File->Copy/Move Photos, and the selected JPG is copied to the folder without the .dop sidecar. (Verification in Finder)
3. Process an ORF raw file in ON1 Photo RAW and export a JPG. From the PM+ contact sheet, select that JPG and via File->Upload send to social media — Flickr, SmugMug, etc. Even through preferences is set so that the .on1 sidecars are not shown in the contact sheet, both the JPG and the .on1 sidecar are selected for upload, and the progress dialog shows an error with one file not uploaded.
4. Copy the same ON1-produced JPG to another folder via File->Copy/Move Photos. Even through preferences is set so that the .on1 sidecars are not shown in the contact sheet, both the JPG and the .on1 sidecar are copied to the target folder. (Verification in Finder)
It seems to me the .on1 sidecars should be ignored in these operations just like the .dop files are ignored.
macOS Catalina version 10.15
iMac (Retina 5K, 27-inch, 2017)
Processor 4.2 GHz Intel Core i7
Memory 32 GB 2400 MHz DDR4
Graphics Radeon Pro 580 8 GB