SharePoint online List view threshold with Macroview

Hi,

Have an issue with list view throttling in Sharepoint online that I need your help with.
The document library has over 87000 items and are categorised into folders and sub folders.
Some of the sub folders item count have reached just above 5k and is giving this resource throttling error.
Have created custom views and indexed on the commonly used columns .
This library is a macroview enabled library and problem arises when we view this in outlook.
ie when you view it in outlook for the first time it loads and can navigate from page to page, but as soon as you sort it through outlook it throws the error.

Any suggestions / recommendations on how to handle folders and sub folders as it is difficult to add a filter .

Many thanks

Shobha