Well, that's what i've been doing for my clients the last 15 years - branding
My point is, "brandable" from a domainer's point of view in terms of collecting them for selling them later is not a promising strategy. Because you basically hope for THAT ONE BUYER who desperately needs exactly that name. While availability of domain names is an aspect in deciding on a brand name, in reality the order is first deciding on a brand name based on several aspects, and then checking if the name is available (or indeed, has to be bought off). But especially nowadays, startups have several alternative options to buying your domain: For instance, they can go with a different brand name, add a suffix, or decide on a different tld. Super especially as nowadays much of the marketing relies on social media and AI and less on rankings in Google search, let alone your website.
In my 15 years of branding experience, i don't think i ever had a client who based their decision on a *brand name* on a nice sounding for sale domain name they happened to stumble across. That's not a thing with real world clients - i consider it to at least partially be a wishful thinking pipe dream amongst domainers. Doesn't exclude the occasional real world sale of course, but i think the majority of "brandable" domains get traded amongst domainers themselves.
In a nutshell, branding in the real world generally isn't based on availability of a for sale domain, but other aspects.