I just got a ROTW latent flame rift off the summoner but I'm unable to upgrade it with
- p ruby
- io rune
- Deep WSS

any idea why??

Are you sure your Sunder Charm is a Latent one? The older Sunder Charms don't upgrade to Renewed at all.

Watch this video and check if your Sunder Charm is actually a Latent Sunder. The old ones can't be upgraded to Renewed:

https://youtu.be/qJezSx5MAlk?t=56

what even is that item? never saw it in d2lod,must be new

Sunder Charms were introduced in September/October 2022 (Patch 2.5 / Ladder Season 2). Blizzard added Sunder Charms alongside Terror Zones. This was the first time in Diablo II history that these charms existed.

The original Sunders were:

Flame Rift
Crack of the Heavens
Cold Rupture
Rotting Fissure
Bone Break
Black Cleft

They broke monster immunities by reducing the monster's resistance to 95%, but they also applied a resistance penalty to the player.

As for Latent Sunder Charms:

Latent Sunders are much more recent and are not part of vanilla D2R. They were introduced in Diablo II: Resurrected – Reign of the Warlock (RotW), where the Sunder system was redesigned into a new progression system:

Latent Sunder → Renewed Sunder

Latent Sunders act as a base version that can be upgraded into Renewed Sunders using Horadric Cube recipes. Additionally, the old Sunders no longer drop in RotW and cannot be converted into Renewed Sunders.

im still scratching my head

It's because you already got a sunder in your inv. Put your own in shared stash and you will be able to do it.

The Renewed Sunder Charm works like a Gheed's. If you already have one in your inventory or personal stash, that's probably what's preventing the Horadric Cube recipe from working.

You can have any number of LOD or latent sunder charms, but you can only have one renewed sunder charm at a time.
The one-per-char restriction applies to annihilus, hellfire torch, renewed sunders and uber ancient jewels
You can't take any actions that would make another one active, like equipping a second item with an uber jewel in it, or picking up a 2nd annihilus, or upgrading a latent sunder when you already have a renewed one.
The one-per-char restriction is separate for your mercenary who can equip an uber jewel of his own in addition to yours