The one thing I'll add about 100% remote companies is that because they operate with much more written collaboration than a traditional company, the application and interview process frequently reflect that.
This is a big part of why you'll very robust application processes upfront. They want to see if you can effectively communicate your thoughts in writing.
I've been interviewing for remote senior engineering positions for the past 6 months and all of them pay significantly below market (market in my case is third-tier 100-person startup in NYC). These were all well funded, well known "remote ok" companies.
Now, it could be I'm overvalued, but afaict nobody is paying SV salaries, certainly not FANG salaries, probably not east coast startup salaries, and in some cases they're not even competitive with boring local companies in small midwestern cities.
* Well-run 100% remote companies - Extremely high application rate, not only because the pool of candidates is much wider (people all over the country and in some cases all over the world) but also because it's a dream job for many of them. In order to deal with that extremely high application rate, the companies need to figure out a way to turn away the vast majority of them as quickly as possible. In many cases, that involves up-front hurdles, like passing tests before you even get a preliminary call with an actual person. But because there is no coordination between companies, you have to jump through the same hurdles for every single application, which makes these opportunities infeasible for a lot of people who just need a job right now. There are a few services, such as Triplebyte, that are seeking to reduce the friction by letting you apply once and qualify for multiple companies, but their support for remote positions is still in its infancy.
* Well-run companies with some remote positions - These positions tend to be those that can't be filled locally because they are too highly specialized. It is uncommon for traditional companies with mostly in-office workers to be looking for remote generalists unless they're growing so rapidly that they can't even find them in their own market. Instead, for these remote positions, you need to have a rare set of hyper-specific skills. Chances are that at any given time, a job seeker will only match those skills for a handful of companies, so it's better if you're just passively looking for new opportunities, rather than actively looking for a new job.
* Poorly run companies or those paying below-market salaries - These constitute the vast majority of remote positions I've seen advertised. They're hoping that the pool of potential candidates is large enough that at least a few will be dumb enough or desperate enough to apply.