Annotated pdf files (Macbook - iPad)

There are a variety of pdf annotation apps and note-taking apps that allow pdf annotation on the App Store. I personally don't use them, so cannot recommend one. I would anticipate that when iPadOS 26 and macOS 26 are no longer in beta, your issue will disappear. In the meantime, discussing beta versions of Apple software here (or anywhere) violates the terms you agreed to for using the software.

There is a free Adobe Acrobat Reader app for i/Pad/OS from the App Store that allows one to open, and annotate PDFs. It is not a PDF editor, unless you pay extra. I use it and don't need the extra editing expense.

You may need the current OneDrive installed on the Mac side too as whether true or false, I believe that files copied to OneDrive are automatically encrypted by it and need to be brought out to the Mac via the OneDrive app to remove that encryption layer so Preview can show annotation changes.

Although I have Office 2021 for Mac home and business installed on Sequoia v15.6.1, I did not install OneDrive.

What app are you using to annotate the file on the iPad? If it's Preview, you'll need to wait to discuss this until iPadOS 26 is launched.