Created attachment 186122 [details] File with an image where you can see the bug At the beginning everything works fine. But at some point and without my being able to appreciate when, the drop-down menus are colored black and the texts are not distinguishable, which remain in their black color.
Please set "Enable Experimental Features" from Tools -> Options -> Advanced and retest. If that resolves this is a dupe of bug 151756 The os/DE color theme support is more completely implemented in the 7.5 release, experimental in the 7.4 builds. You can also test with with a parallel install of 7.5.1 or nightly master against 7.6, see the Wiki -- https://wiki.documentfoundation.org/Installing_in_parallel
I am working on Windows 10 with libreoffice 7.4.6.2 (in principle more stable version). My path is a bit different: tools, options, advanced, enable experimental settings, check the box. I restart LO, in this case writer works in dark mode. As I prefer not to have experimental settings enabled, I disable it again. I restart LO and it opens in classic mode. After several days without problems, the drop-down menus have a black background again and so do the letters. I restart LO and it is fixed, but I can't locate the action that leads to this problem in the colors. Maybe it can influence (I have not checked it): locale Spanish but libreoffice texts in English; this leads me to sometimes press Ctrl-N instead of Crl-B. Well, if you can give me some advice, I'd appreciate it. Otherwise I will be patient and wait for the next releases. You will notice that I don't speak English, sorry for the additional difficulty for you.
[Automated Action] NeedInfo-To-Unconfirmed
Sorry, nothing to be done for 7.4 and already corrected for LO 7.5 Upgrade to LO 7.5.2 just released.
In case you find it useful for future releases, I think the problem arises when I work with LibreOffice and QGIS Layout Manager at the same time. In principle, I think that the two applications work with their own version of Java, but it is as if there was some interference.