The extension is probably not broken because of Firefox but because Flatpak's sandboxing prevents it from talking to KeePassXC.
I'm not sure about the frequency but on Linux you sometimes get small (few megabytes) updates to the shader cache but multi-gigabyte updates are just normal Rocket League updates (or I can't think of any other reason).
I too have Rocket League on Steam running on Linux but I haven't noticed any frequent big updates. Not anything out of the ordinary.
Psyonix ended Mac and Linux support but you can still play Rocket League (the Windows version) on Linux via Proton (a compatibility layer that translates Windows specific calls to their Linux equivalents). You can even run BakkesMod alongside it.
I believe this is Steve Huffman (aka u/spez) the co-founder and CEO of Reddit. (wikipedia)
This controversy is what this post is most likely referring to.
The title is perhaps a bit misleading. It's not a version of ChatGPT. At least not in the sense that it's a version of OpenAI's ChatGPT.
gpt4all: an ecosystem of open-source chatbots trained on a massive collections of clean assistant data including code, stories and dialogue
It's an ecosystem. They seem to have GPT LLMs (Generative Pre-trained Transformer Large Language Models) and a chat app to interact with those models. Also they say that the models can be run on consumer grade CPUs (this is where the locally hosted part comes in to play).
I suggest you read the original review the article is refering to. It's more detailed and very well.l written.
I don't know about DLSS specifically as I don't have a Nvidia GPU but AMD FSR works fine as long as you use a somewhat new version of Proton. (And FSR isn't limited to AMD GPUs)