how to downgrade 10.14.6 to 10.14.4

Look into the Free LibreOffice, it handles MS Office files…

https://www.libreoffice.org/

Apple macOS (Mac OS X)

The software and hardware prerequisites for installing on a Apple macOS computer are as follows:

• LibreOffice 6.3.x: macOS 10.10 (Yosemite) or higher
• LibreOffice 6.2.x: macOS 10.9 (Mavericks) or higher
• Intel processor
• 512 MB RAM
• Up to 800 MB available hard disk space
• 1024x768 graphic device with 256 colors (higher resolution recommended)

It is a recommended best practice to back-up your system and data before you remove or install software.

Notes:

• For certain features of the software - but not most - Java is required. Java is notably required for Base.
• Due to an issue, there are the following restrictions with Java: on macOS 10.10 and newer, JRE isn't found, JDK is required
• LibreOffice 4.3 can still run on OS X 10.6+, but please understand that this support ended when 4.3 was retired on May 27, 2015.

https://www.libreoffice.org/get-help/system-requirements/#Apple

Feature Comparison of LibreOffice v6.4 with Office 365/Office 2019 for Mac

https://wiki.documentfoundation.org/Feature_Comparison:_LibreOffice_-_Microsoft_Office

Just follow the steps here for "Restore both macOS and your files":

Restore your Mac from a backup - Apple Support

Choose a date for the backup prior to the update.

Specifically what software are you having problems with? p

Also have you run any "cleaning", "optimizing", "speed-up" or anti-virus apps?

Only way would be if you have a Time Machine backup with 10.14.4.

No.

You're welcome. That's good news!

Good news, stay safe! :)