I don't think I've seen a single episode of the Pokemon anime produced after its first year on US television.
I have seen episodes of post-Indigo Pokemon anime. Still, this post does point to how fascinatingly funny it is that even though Ash was the main character of the Pokemon anime for so long, the vast majority of his show past the original series is really obscure and niche. Even nowadays in the streaming service era most of it is lost to time, and you're rarely going to find anyone with in-depth knowledge of what happened in Ash's story past the Ash/Misty/Brock era.
Journeys is the only Ash-era season that's easily accessible besides OS nowadays, since it's on Netflix, and I imagine Pokemon GO and Goh's existence combined with Ash finally getting his big win and being allowed to leave have made that season more memorable in a way, but everything that came in-between? No shot. You're gonna be hard-pressed to find it anywhere, and ask your average layperson about anything that happened between the original series and Journeys...and they probably won't know much. There's some shot a person might know about, say, Serena or Dawn, but even those two don't reach the pop culture level of iconic that Ash's OGs did.
And frankly I don't blame anyone for the fact that things turned out that way. Most of the stuff that came between Gens 3 and 7 for Ashnime ranges from bland and boring at best to borderline unwatchable at worst. You could cut a very significant portion of Ash's 1000+ episodes in the show out of existence and lose absolutely nothing in the process. Ash staying that long and a lot of his show being an endless tango of mediocrity dropped his reputation into the gutter. I grew up in the Gen 4 era but back in my middle and high school days in the 2010s I would sometimes talk about Ash with my IRLs and the conversation would always boil down to "Yeah the show sucks lol" and making fun of Ash.
Which is to say, I'm glad that Ash's run on the show is finally over. I enjoyed Journeys, and I'm glad they finally ended him there. Horizons is the first series of the anime that stars a new protagonist, and Liko is genuinely a great character. I really enjoy watching her. Seeing her story unfold really shows how much keeping Ash for so long stifled the anime's potential. Watching it on Netflix has been a real treat over the past year or so (and I do watch the original Japanese through...means I shall not speak of here).
Going back to what you said, I think that applies to a lot of people. The Indigo League and Orange Islands seasons seem to be the only seasons of Ash's story (at least pre-Journeys) that have genuinely withstood the test of time in the greater public consciousness. The vast majority of his show just faded into obscurity and most people didn't really pay attention to them. And looking back, especially in hindsight now that I get to witness a totally new story from the Pokemon anime, and I look back at most of the post-OS Ashnime particularly from AG to SM and I'm like "Wow...yeah this fucking
sucks". Even the better parts of those were carried hard by other characters like Dawn or Paul or whatnot...not Ash. I don't ever wanna touch a lot of that again. So I don't really blame a lot of people for not knowing much about those seasons. They did suck and it showed.