Here’s a basic explanation of the Timbs v. Indiana holding.
Mr. Timbs convicted of selling a small amount of heroin. (Small enough that he was not sent to prison - instead he was sentenced to a year of home detention and 5 years of probation)
He was arrested while driving an SUV he had bought for about $42K, with money he received from a life insurance policy when his dad died. (So no claim that the car was bought from drug profits).
The trial court in Indiana denied the claim for forfeiture, holding that the value of the SUV was " grossly disproportionate to the gravity of Timbs’s offense" and thus that forfeiture would violate the 8th amendment prohibition on excessive fines.
The state appealed, and the intermediary state appellate court affirmed – but then the state supreme court in Indiana reversed, holding that the 8th Amendment excessive fines prohibition applied only to federal action, not state.
This is where it gets a little tricky. The federal bill of rights (first 10 amendments to the US Constitution), as written, does apply only to federal actions – but there’s a long line of cases throughout the 20th century that chipped away at this, holding that the protections are extended to the states via 14th amendment. (“No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws.”) This is called “incorporation”. Wikipedia explains it very well here: https://en.wikipedia.org/wiki/Incorporation_of_the_Bill_of_Rights
So one by one, over time, almost all of the provisions of the bill of rights have been held to apply to the states, including the 8th Amendment prohibitions against cruel and unusual punishment and excessive bail. Courts have pretty much assumed that the prohibition against excessive fines was also incorporated. (8th Amendment = "[e]xcessive bail shall
not be required, nor excessive fines imposed, nor cruel and unusual punishments inflicted.”) But the Supreme Court had not yet expressly held this to be the case.
So in Timbs you have these facts: The trial court determined that the civil forfeiture was an excessive fine that violates the 8th amendment – but the state supreme court said that didn’t matter, the state of Indiana doesn’t have to obey the 8th Amendment. Now 9 Justices of the US Supreme Court all agree that the 8th Amendment DOES apply – and in this case as there already is a determination that the forfeiture was excessive.
An interesting technical wrinkle is that while all 9 justices agree that the 8th Amendment prohibition on excessive fines applies through the 14th amendment, but there is a little bit of a quibble as to whether this is because of the “due process” part of the 14th amendment (as the court held), or whether it would be better to put this under the “privileges and immunities” part (a rationale that Justices Gorsuch & Thomas would prefer).
Nothing about this case sets any sort of guidance or bright-line test as to whether a particular fine or forfeiture would be excessive – that is something that pretty much gets decided on a case by case basis.