A common technique to prevent fast fragmentation of indexes (and thus improve performance) is to specify a custom fill factor on a particular index (e.g. 80-99).

In AX2012, this could be controlled from within the application (System Administrator module -> Periodic -> Database -> SQL Administration). This functionality is no longer available in D365FO, also no not in an alternative way (e.g. LCS), resulting in all indexes to have a 100% fill factor.

There's currently no (supported) way to control the fill factor. Even if the fill factor is changed directly on the database (possible, if you're creative), it's not going to stay like that: a database sync may overwrite the index at some point and thus set the fill factor again to its default (100%).

Requesting similar functionality as what is available in AX2012 to control per index fill factor within the application. The custom fill factors would then be used when running the "Database index rebuild system job" batch job.

More information (AX2012):
https://docs.microsoft.com/en-us/dynamicsax-2012/appuser-itpro/tune-data-access-settings
https://www.kevinroos.be/2017/06/dynamics-ax-fill-factor/
https://kaya-consulting.com/index-fragmentation-effects-on-performance/