It looks like you was using the MS Edge legacy browser to edit the PDF files and you was using the Highlight feature in it.
See here:
After that it looks like you start using the MS Edge (Chromium) browser. The Highlight feature was missing in the previous versions of the MS Edge (Chromium) browser and only the Draw option was available.
The Highlight option has been added to the latest version of the MS Edge Stable channel. I am using the MS Edge 85.0.564.44 version and I can see the Highlight option.
See here:
I suggest you update the MS Edge (Chromium) browser to the latest version may help you to get this feature.
Let me know if I misunderstand anything in your above mentioned description. I will try to correct myself and try to provide you further suggestions.
Thanks for your understanding.
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