How to file a complaint if your game account has been stolen

Is there any way for me to retrieve the high-value currency and props that are gone

You can email support, but I doubt they will restore anything they typically don't interfere with the economy and all that.

GGG doesn't return stolen items.

If you've lost access to your account entirely or they bound an email to a steam/etc account (which you can't remove yourself because they'll send a confirmation link to the thieves email, and will periodically use it to steal any new currency you earn) emailing GGG is the only option.

Unfortunately it's not a great one either. They'll immediately lock the account entirely because it's ownership is in dispute. The problem is that it takes several email exchanges for them to verify that you are the account owner, and the post POE2 backlog on complex support requests means they're running about a month between messages. (See all the "my account has been locked for several months" threads in this forum if you doubt me.)