Help for sending email is at: https://help.libreoffice.org/7.5/en-US/text/shared/optionen/01020300.html?System=UNIX&DbPAR=WRITER&HID=cui/ui/optemailpage/OptEmailPage#bm_id7723015 (why it's different when called as https://help.libreoffice.org/7.5/en-US/text/shared/optionen/01020300.html ? ) It should explain more how mail can used. Like: "Supported are thunderbird/icedove, seamonkey/iceape, netscape/mozilla, evolution, kmail, groupwise, sylpheed/claws, dtmail, gnome/geary?, and command client mutt. If email program is not specified here, default system email program is used via xdg-email or kde-open". https://opengrok.libreoffice.org/xref/core/shell/source/unix/misc/senddoc.sh iceape (seamonkey), icedove (thunderbird) were Debian rebranded clients but are long unmaintained. Only SeaMonkey is actual. I'm not sure what "gnome" is, or is geary supported. https://wiki.documentfoundation.org/Faq/General/033 is out of date. This help page should also be related to https://help.libreoffice.org/7.5/en-US/text/shared/01/01160200.html.
Bug 116211 says "Help (on tools/options/internet/email) is not at all helpful".
Also https://help.libreoffice.org/7.5/en-US/text/shared/guide/email.html says: "Working in LibreOfficeDev, you can send the current document as an email attachment. Choose File - Send - Email Document. LibreOfficeDev opens your default email program. In your email program, enter the recipient, subject and any text you want to add, then send the email." But it should link to Help that explains about configuring email. Also should be added issue of using webmail, as raised in bug 70961. There I wrote that another local program should be used to communicate with webmail, so that LO uses it as it's supported program.