Unable to select and edit small/er text. Text glitches out.

You may also want to work through Adobe’s GPU troubleshooting guide, as display and selection issues like this are often related to GPU rendering:

https://helpx.adobe.com/illustrator/kb/illustrator-gpu-performance-driver-update.html

If the issue disappears when using Preview on CPU or after disabling GPU Performance, that would strongly point to a rendering-related issue rather than a problem with the document itself.

So it’s not just a single file, it’s happening in multiple files?

With specific fonts or different ones?

Do you have font management installed? If so, which one?

This doesn’t look like a normal performance issue. The text corruption in your second screenshot suggests Illustrator is failing to render the text correctly, rather than simply slowing down.

A few things I’d check:

• Switch to View > Preview on CPU. If the problem disappears, it’s likely related to GPU rendering.
• Try Reset Preferences (hold Option + Command + Shift while launching Illustrator on macOS).
• Test whether the issue occurs with a brand-new document or only with this particular file.
• If you’re using a variable font or a recently activated Adobe Font, try replacing it with a standard system font (for example, Arial or Helvetica) to rule out a font-specific issue.

Since you mentioned this happens mainly in documents containing both very large and very small artwork, it would also be useful to know:

• Which version of Illustrator are you using?
• Which macOS version are you running?
• Are you on Apple Silicon or an Intel Mac?

Adobe also has a couple of articles worth checking:

• Reset preferences: https://helpx.adobe.com/illustrator/kb/preference-file-settings.html
• Troubleshoot GPU and display issues: https://helpx.adobe.com/illustrator/kb/illustrator-gpu-performance-driver-update.html

If switching to CPU Preview immediately resolves the issue, that would strongly suggest a GPU rendering bug rather than a problem with the document itself.