Vintage, Obsolete and other terms have existed for years, this isn't new whatsoever. So what if they don't want to do the battery? Let them lose the revenue and take it somewhere else or do it yourself. This is 2023, nearly 2024 we have guides, access to parts and tools. There's no reason not to get it done.
Okay, so Apple is hellbent on not allowing other stores to fix or replace parts, but at the same time they leave customers in the dark with perfectly decent laptops.
You're confused, there are authorized and non-authorized repair centers. There's also nothing proprietary about doing a battery. Do not confuse a battery replacement on a laptop for displays on a phone - they're different.
All these batteries you find will only be online, you're not gonna get it offline you have to order it bud. Or you can take it to a shop - they have to get the parts. That's their problem not yours.
ifixit battery if you want another method.
Here's the guide in written form, and here in video form and here