I might be able to offer a perspective “from the inside” that would be helpful. My day job is the director of electrical engineering for a mid-size (non-aviation) international company that designs and builds electronic products that are similar in complexity to avionics. I do not have any affiliation with Garmin other than owning some of their gear, but as someone who works with similar technology I would give them kudos for 25 years of support. That is nearly unheard of for digital electronic products and very difficult to achieve at a practical level.
The Garmin statement that some components are not available rings true for me. The past couple of years have been a nightmare in the electronics industry, with shortages and obsolescence of many components. Not just “chips” as you hear about in the news, but nearly every other type of component as well. In complex electronic designs there are often critical components for which there is no substitute available at any price. If the supplier quits making that unique item you can no longer build or support the product. My company has found itself in that position recently with some products and I have no doubt that Garmin has too.