There is a bug on the Advanced search UI where the search phrase is not visible when typed.

Acrobat Pro DC
Architecture: x86_64
Build: 20.9.20067.384717
AGM: 4.30.101
CoolType: 5.14.5
JP2K: 1.2.2.46033

MacOS Catalina Version 10.15.4

To reproduce
1) Open Acrobat Pro DC
2) Go to Edit -> Advanced Search
3) Search for "All PDF Documents in" in a selected folder
4) Start typing in search keywords or phrase
5) Click on some results and open the corresponding PDFs
6) Select "New Search"
7) Type in a new search keyword or phrase

Bug observation
8) You will observe that the cursor moves along with the entered text, but the text is not visible.