When I was writing that, I was thinking of other platforms. For example: I had a GP2X at one point, which was a handheld console that ran Linux. It clearly wasn't a mass-market device, but it was an open platform with plenty of development tools. It should have been the sort of thing that appealed to homebrew developers. It was appealing for some, but it was up against the Nintendo DS with flash cartridges. There were almost certainly more flash cartridges than GP2X's in the world, even though they were a grey market item (at best). They didn't have a chance, and I think they only managed to produce one successor before going out of business. (Of course, there were other factors. This was right around the time of smartphones becoming popular. Smartphones may have crumby controls for gaming, but at least anyone could develop software for Android and the barrier to entry was relatively low for iOS.)
The Steam Deck, well, that has other things going for it. Yes, it is an open platform. Yet it, along with similar devices, are also PC compatible. That makes it appealing to developers, may they be developing games for Linux or Windows. Perhaps the biggest thing going for it is being backed by Valve, which is large enough to coexist with Nintendo and is unusual for a larger company in that they value an open ecosystem. To understand how unusual that is for a large player entering the market, just look at the original Xbox.
The Steam Deck, well, that has other things going for it. Yes, it is an open platform. Yet it, along with similar devices, are also PC compatible. That makes it appealing to developers, may they be developing games for Linux or Windows. Perhaps the biggest thing going for it is being backed by Valve, which is large enough to coexist with Nintendo and is unusual for a larger company in that they value an open ecosystem. To understand how unusual that is for a large player entering the market, just look at the original Xbox.