Private use area unicode ligatures (U+E000 - U+F8FF) not displaying on Microsoft Office 2021 programs

Question

I have created an OpenType font containing established unicode points (Latin, Greek, Runic) & custom characters in the private block unicode points of the range U+E000 - U+F8FF.

Part of this involves ligatures. Mainly these are two characters separated by a zero width joiner (U+200D) or characters followed by a combining character (e.g. combining acute accent U+0301).

The combining character ligatures behave properly, but the zero width joiner ligatures only work on the established unicode points in Microsoft Word 2021, not on any private area unicode nor in a combination of the private area characters and the characters in the other blocks.

The results are variable between Word, Excel, Powerpoint and Publisher - please see the attached screenshots for examples. I have created a very simple font to showcase the problem, please see the following link in order to download the font (Alt + x with the following unicode to insert each character):

https://drive.google.com/file/d/1ItxMiHXOW4naP6S7bGg7QiBGsOFbwEcy/view?usp=sharing

The code points covered are:
A - U+0041
B - U+0042
C - U+0043
 - U+E000
 - U+E001
 - U+E002
́ - U+0301 (combining acute accent)
‍ - U+200D (zero width joiner)

In the test font two characters can be combined using the zero width joiner (U+200D), and the characters (or the combinations) can be combined with the combining acute character (U+0301). U+E000 - U+E002 are from the private unicode block.

On Microsoft Word when highlighting the text that I want to have ligatures => selecting font => selecting advanced and in OpenType features setting => ligatures to all - it shows them correctly in the preview, but nothing changes when pressing OK. They do not display properly on the virtual document nor when printed. On Publisher they do not appear correctly in the preview either.

I imagine that perhaps this is some sort of security feature? Perhaps to avoid the malign substitution of text through a dodgy font, but in this particular case it is very annoying. It is an issue that more basic word processors do not seem to share, but as I would like to continue using Microsoft Office, I could really do with a fix.

Is anyone able to offer any help or further insights? Many thanks.