There will be no further developments in 20.9 so don't expect any Libreoffice update (@ the official repository). You may try to manually install the version you found out to be working as you want.
deepin Thanks for your reply. Installing applications not from the app store sometimes leads to system failures, for example Google Chrome. Therefore, I did not take any chances, but a newer version of Libreoffice was found in the app store - 7.5.7.1. Updating on top did not work - the old version was indicated in the help of the installed application, but the problem disappeared. I completely deleted the LibreOffice and installed it again. And then I returned version 7.0.4.2 again via the terminal and the apt cache - its interface is more convenient for me. There was also no problem with displaying page numbers. I attribute this behavior to possible damage to the Writer application dependency when cleaning the system.
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How to create shortcut like in Windows? 
Hello. In the LibreOffice 7.0.4.2 Writer application, when numbering pages, the name of the field appears in the footer of the document instead of the number. When converting a document to *.pdf format, page numbers are not output - only the name of the field. I used the LibreOffice 7.6.2 Writer application from the Ubuntu 23.10 installation disk in live mode - there the document opened immediately with numbered pages. Accordingly, they remained when converting to *.pdf. Previously created documents in previous versions that have page numbers in the footer, now in Deepin 20.9 also open only with the field name instead of the number.