There is no visible keyboard focus indicator with either gtk3 breeze theme or kf5 breeze theme. Gtk adwaita somehow manages to draw a thin dotted line. Problem in general is, that since #i110915#, flat buttons don't send a focus update. This is no problem, if you rely on LO to draw a dotted focus rect, like for gen, or support ControlType::Pushbutton + ControlPart::Focus native, which both doesn't fit the bill for kf5. Proposed solution is to send a focus update in this case. Gtk+ uses the separate ControlPart::Focus notification.
Jan-Marek Glogowski committed a patch related to this issue. It has been pushed to "master": https://git.libreoffice.org/core/commit/3f7515258e91266f10e5c7bafee2d3d6fa9c91c2 tdf#137660 send some focus event for push buttons It will be available in 7.1.0. The patch should be included in the daily builds available at https://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More information about daily builds can be found at: https://wiki.documentfoundation.org/Testing_Daily_Builds Affected users are encouraged to test the fix and report feedback.
Jan-Marek Glogowski committed a patch related to this issue. It has been pushed to "libreoffice-7-0": https://git.libreoffice.org/core/commit/c425987e15519a9187fd482502f908b54c8416cb tdf#137660 send some focus event for push buttons It will be available in 7.0.4. The patch should be included in the daily builds available at https://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More information about daily builds can be found at: https://wiki.documentfoundation.org/Testing_Daily_Builds Affected users are encouraged to test the fix and report feedback.