A family of Microsoft word processing software products for creating web, email, and print documents.
OK, in the first thread you cited (https://answers.microsoft.com/en-us/msoffice/forum/all/word-office-365-equations-strutures-not/094b0830-be2b-4e67-8413-c182b6d0c904), the various equation structures, such as trigonometric functions, are missing completely. I'm not seeing that here. On the contrary, all options are available.
In the other thread you cited (https://answers.microsoft.com/en-us/msoffice/forum/msoffice_word-mso_win10-mso_o365b/word-equations-bar-load-very-slowly/1bcf248b-5b65-461a-91e0-b12ab2bdfe1c), Word populates the galleries slowly. I'm not seeing that here, either.
As you already know, suggestions have been made in the past, for systems where these symptoms appear, and those include repairing Office and setting the default printer explicitly (rather than relying on the functionality in Windows 10 that changes the default printer based on the currently selected printer). Since these workarounds help on your system, you should make use of them.
More importantly, you should report what you are seeing via File > Feedback > Send a Frown in Word.