Elden Ring's developers know most players use guides, but still try to cater to those who go in blind: 'If they can't do it, then there's some room for improvement on our behalf'

To be clear, it's weight of equipped items. You can have as much stuff as you want in your backpack.

The UI will show your equip load (as a percentage in newer games), and how it changes when you change equipment. Note that some rings are surprisingly heavy.

I think there's a breakpoint at 70% where your roll gets worse.