The Formula bar input line is lower than the other fields on the formula bar so any input is hard to read unless the formula bar is expanded. Happens on new and existing spreadsheets.
Would you say this picture describes your issue? attachment 184049 [details]
If so, the bug is already reported in bug 151682 and it would be great if you could test a recent master build and report if you see it fixed in there: https://dev-builds.libreoffice.org/daily/master/current.html
Yes that is exactly the same problem. The master build Win-x86_64@tb77-TDF did fix it.
*** This bug has been marked as a duplicate of bug 151682 ***