Created attachment 173837 [details] a docx file of MS office It fails to open a .docx document.
On pc Debian x86-64 with master sources updated today, I could reproduce this. It seems there's a never ending loop in https://opengrok.libreoffice.org/xref/core/sax/source/fastparser/fastparser.cxx?r=ceef618f#1091
I transformed .docx files through online service to .odt and they were opened.
repro with Version: 7.5.0.0.alpha0+ / LibreOffice Community Build ID: af2879e434fa0dc6b2a626617ed865e4f66eb5ad CPU threads: 4; OS: Linux 5.11; UI render: default; VCL: kf5 (cairo+xcb) Locale: en-US (en_US.UTF-8); UI: en-US Calc: threaded