I had been using Office 2011 (Outlook, Word, and Excel), then "upgraded" to Office 2016. But back in August, I experienced a serious issue with Outlook 2016 on my Mac Mini (could not read its "database", yet I was able to view my EMails on my ISP's (Comcast) site). So I "ditched" Outlook 2016 on both of my Macs for the excellent free EMail client Thunderbird, and have not looked back. Then, back in early October, I decided to replace the remaining Office 2016 "stuff" (Word and Excel) with the excellent free suite LibreOffice, and it works like a charm in both High Sierra and Mojave. And its Calc spreadsheet application has easily opened all of my Excel documents. Similarly, its Writer Document has easily processed all of my Word documents.
So, I strongly recommend LibreOffice, available from here:
https://www.libreoffice.org/
A similar stellar one is OpenOffice, available from here:
https://www.openoffice.org/
The differences between the two are 1) LibreOffice has a larger array of formats it can process (ie, both read and write), and 2) with OPenOffice, one can pick and choose which modules to install. With LibreOffice, one needs to have all of them installed. But it does not take up much space. In fact, on my Mac Mi ni (the machine I am using now), it is only 732 MB in size.
Again, the two modules I primarily use, Writer Document and Calc spreadsheet, work flawlessly under both High Sierra and Mojave. ( suspect the same is true for OpenOffice.