What’s the difference between ARM and x86 other than proprietary?
Both ARM and x86 are proprietary, innovation is made differently tho.
Arm holding set new standard for the broader concept of innovation, trying to gather as many companies possible to further innovate in their own way and as many companies possible.
X86 is mostly ruled by Intel and the way Intel manufacture things; AMD is thrown in the mix both both need to be cautions around their business: it's in their hope no third party interfere with what and how X86 are manufactured.
RiscV is the ultimate goal: a platform not owned by anyone, which anyone is free to innovate for their propose (like Linux's kernel which power big Super Computers mainframes, desktop pc or table clock: there's a root capability, then everything extend from there by its purpose.).
How is steam an ARM store? (Genuine question not a disagreement)
It's not an ARM store in the sense they sell ARM hardware; but the store itself (also) runs on ARM CPU: to have a piece of software (such as Steam, as the steam client you download and install) run on different platform, you need some work to be done: CDProjekt did the job for CyberPunk 2077 (for the Nintendo Switch 2) as Valve did the job for Steam (for the MACs)
What specific brands/companies/developers do you see becoming relevant in this context within the next year?
Intel could come in to play, the reason they are not "seriously" in the RISC business is because the conflict of interest with "their" X86.
Both Nvidia and AMD are already in both ARM and RiscV business.
Any company in the smartphone business can join in: they just need ARM binaries (CPU) and full Vulkan support (GPU)
Will this translate to more budget friendly pc-gaming options?
You can buy a ARM Raspberry Pi Zero 2 (and alike) for about ~15$, add this a MicroSD, a K/M and a screen to attach to hdmi, and you have a fully fledged Linux PC with basic office capabilities.
I am a former pc-gamer. Built my last PC in 2009. Even then it was a budget build (AMD gfx).
A Raspberry Pi 4 B 2GB would cost about ~40€ (there are cheaper chinese variant) would match a 2009 Intel Core 2 Duo, 2GB ram and ATI Mobility Radeon HD 4330. You can power it with a powerbank.
It's not like Devs can afford to say "Hey, you! No, not you, the other one.... hire me now!"