https://www.libreoffice.org/download/download/?type=win-x86&version=6.3....
I think I'm running 6.2.6 now and would like to check out 6.3.0 - they said the performance improved greatly.
Microsoft Office is going completely subscription model now so there's very few alternatives for free or one-time pay office suites.
As always, you can report and follow along the progress of new releases in the Outdated Apps Thread: https://portableapps.com/development/outdated
You can find this linked in the Development and Support section as well as a banner at the top of the page when creating a new forum topic.
Sometimes, the impossible can become possible, if you're awesome!
You can find it here https://sourceforge.net/projects/winpenpack/files/X-LibreOffice/releases/ since 10 days.
Based on former releases, you must wait round about 4 weeks more, before you can get it on portableapps.
That's an unofficial build not hosted by The Document Foundation that doesn't have the full feature-set of LibreOffice Portable (it also doesn't automatically install or automatically update). The official LibreOffice Portable 6.3.0 and 6.2.6 Still have both been built and sent to The Document Foundation for approval and hosting, but how long it takes them to post it varies.
Sometimes, the impossible can become possible, if you're awesome!