Problems with High Sierra VM using Parallels 26 running Sequoia

I need a stable, production system running Sequoia as the desktop and High Sierra as the guest VM. (The computer is a 2017 iMac Pro, which natively can run High Sierra.) Everything is loaded, and I used the Migration Assistant to update the High Sierra system from a time machine backup from another High Sierra system. The Sequoia desktop runs beautifully on the iMac Pro with no problems.

The High Sierra VM mostly seems to work, although it's very slow and the cursor freezes frequently. The screen resolution is low (1024x768) and settings don't improve it. However, the big problem is the 32-bit version of Pages, which is the whole reason for this exercise. Pages (and Numbers) will start, but when I display or create a document, the document window appears but remains blank no matter what I do. The document is actually there because as I click around in the blank window, if I happen to click on an invisible formula, for example, it displays. But the document itself remains invisible.

I installed Parallels 26 Pro and the toolkit. Is there a problem with version 26 running 32-bit apps? Should I downgrade to a different version? Is there something else I'm missing?