As others have stated you have 2 versions of LibreOffice installed. One is the 25.8 version which is what you see in the start menu. The 26.2 is not in the start menu. Too fix this you need to uninstall both versions.
Open the start menu and select Software. Wait for it to finish loading then click the search button in the top left corner and enter libreoffice.
Note the case of item names. LibreOffice vs libreoffice.
You must uninstall the 26.2 version first.
Select the item named LibreOffice. This is the 26.2 version. Uninstall it.
Do not uninstall the item named libreoffice yet which is the 25.8 version.
Uninstall each module that shows Installed. Writer, Draw, Impress, Calc, Math, Base.
After uninstalling the modules select and uninstall libreoffice.
Close the software manager. Right-click on an open area of the desktop and select Open in Terminal.
Enter each command exactly as shown.
Enter:
sudo apt-get remove --purge "libreoffice*"
Press enter
Enter your password.
Press enter
Wait for it to finish.
There will be a prompt asking if you want to continue.
Press y then enter.
Wait for it to finish.
Enter:
sudo apt-get clean
Press enter
Enter:
sudo apt-get autoremove
Press enter
Close the terminal and reboot/restart your computer.
You may have to authenticate up to 3 times.
Wait for your computer to finish starting.
Open the start menu and select Software. Wait for it to finish loading then click the search button in the top left corner and enter libreoffice.
Select the item named LibreOffice. Note case.
Scroll down to the version box and confirm 26.2
Go back to top. Under the Install button confirm Flathub is selected. If not click the triangle and select Flathub.
Click Install.
After installation is done you can click the Launch button in the manager or go to start menu - office and click LibreOffice.
Click Help - About LibreOffice and check the version.