net-misc/nextcloud-client-3.0.2 が dev-qt/qtwebengine-5.15.1 に、そしてそれが dev-lang/python:2.7 に依存していてという状況
で、元凶の nextcloud client はこんな issue や PR がある:
Build without qt-webengine · Issue #932 · nextcloud/desktop
https://github.com/nextcloud/desktop/issues/932
Add support for compiling without QtWebEngine (webflow / flow2 support) -- rebased by theova · Pull Request #2204 · nextcloud/desktop
https://github.com/nextcloud/desktop/pull/2204