There is a difference between security guards and loss prevention officers.

According to the law and applicable case law relevant here, all private proprietary security officers are private citizens acting under the Shopkeeper's privilege. Unless you are a peace officer acting as a peace officer, you are treated as a private citizen.

There are many retail stores and chains that will forcibly detain you, and it is perfectly legal.

It is perfectly legal. That was never in dispute. You and your employer assume full unlimited legal liability by doing so. You can be sued because of it and lose your job as a result. There are no protections offered under the Shopkeeper's privilege or relevant case law. We were only trained for Washington, Oregon, and California though. They gave us specific case examples, taught us the circumstances, and taught us what happened as a result. If you put your hands on someone, you assume liability for doing so.

Don't confuse something being legal with someone's ability to take your house for doing it.