Is Voice of Reason still ladder only?

Nope, for Diablo 2 Resurrected it's available in nonladder now.

You can click on this page on "Database" and on "Runewords" to see the list of all runewords. It's noted if a runeword is ladder only.

While i'm not going to guarantee anything, this site says it's not:
https://fabd.github.io/diablo2-runewizard/

This site, right here, also specifies if an item is Ladder or not. If you go to the runeword page, at the bottom of the stat box it will say "Ladder Only". If nothing is there, its available in Non-Ladder too.

Like others have said, Voice of Reason is no longer ladder-only in D2R. That said - as far as I know, it is still ladder-only in LoD, which is still a playable game (and some still play it), so you need to be sure that whatever website/resource you're checking is actually updated for D2R if you're looking for D2R information. Not all websites/resources are updated for D2R. There are more differences than what is ladder-only. Skills have been rebalanced, new rune words have been added, skill cooldowns and NHD has been reworked,

Terror zones and sunder charms are a new thing, some old bugs have been fixed, and other things. I'm not sure if there's a comprehensive list of all changes (but you could look at all D2R patch notes.)

VanKronau wrote: 3 days ago

According to fandom, Voice of Reason is ladder only. But it was introduced in patch 1.10, which seems to be much in the past.

Next time please update such outdated information.

These are the currently 8 ladder-only runewords:
runewords/#filter=Ladder%20only

In d2R, only the runewords of patch 2.6 is ladder only.

For future reference: if you have any offline characters then they can also make ladder-only runewords in D2R.