The experimental feature's "Show outline content visibility button" checkbox in Tools ▸ Options ▸ LibreOffice Writer ▸ View dialog is not visible even if "Experimental functions" is enabled and LO is restarted.
Also in Version: 7.1.5.2 / LibreOffice Community Build ID: 85f04e9f809797b8199d13c421bd8a2b025d52b5 CPU threads: 8; OS: Mac OS X 10.16; UI render: default; VCL: osx Locale: en-GB (en_GB.UTF-8); UI: en-US Calc: threaded