I saw somebody recommend it in another topic but I can't find it anywhere in the Weapons Guide (I've tried Tier 7 weapons but no luck)

Subeta Lodge has this at the bottom of item information - Weap Notes: Incomplete information. Tier 11-12 Attack: 11-12 physical, 11-12 earth, 11-12 fire block 15-25 light heal 8%

Does this mean it's a scaling weapon or the damage only goes up when a pet is Tier 11?

I'm not sure. It could be that weapon only scales to Tier 11 because there's also the that starts as a Tier 11 weapon and has incomplete information as well. That one may end up scaling for higher tiers while the blade is for slightly lower tiers, but I'm not sure about that.

I've tried doing a google search for it but couldn't find any further information

Iirc, it scales between Tier 7-9. I'm trying to find more information for you, but I'm having a bit of trouble. If I still can't find anything, I'll just test it using my own pets. Unfortunately, it would only be for T7 and T9+ as I don't currently have a T8.

[edit]My testing:

T7 Attack: 7-8:dmg:physical: 7-8:dmg:earth: 7-8:dmg🔥 (21-24 icons) Defense: 7:block:light: Heal: 7%:heal:

T9+ Attack: 11-12:dmg:physical: 11-12:dmg:earth: 11-12:dmg🔥 (33-36 icons) Defense: 15-25:block:light: Heal: 8%:heal:

Thanks.