Please forgive me, I thought it was the function of a plug-in. Could you put the split screen function button at the top of the PDF file, which might be more convenient?
There is a plugin that puts the two split-view icons in the top taskbar (albeit being primarily a plugin for extracting reference lists from PDFs) ... https://github.com/MuiseDestiny/zotero-reference
https://github.com/MuiseDestiny/zotero-reference