A good way to approach these opportunities is to understand the nature of the opportunity pool. Perhaps the most famous resource on this topic is a video about trimodal compensation distribution by Gergely Orosz[0] (a former Uber engineering manager), which talks about the different types of companies operating in Europe (i.e. local, european, global) and their compensation bands
A thing to note is that even though tech companies are now more open to hiring outside of SV, in the grand scheme of things they still represent only a minority of employers as you travel further out the globe. Which is to say: the opportunities do exist in Europe, but they're not going to come on a silver plate for everyone. As a software engineer, you'll need to put some work in a) finding these employers and b) preparing for their interview structure (which is often said to be difficult to pass)
It is true that these companies used to prefer relocation to US (which require a visa w/ bachelor degree requirements, in addition to the actual willingness to relocate), but now thanks to covid, companies are often willing to hire in Europe (and even as far as India) even despite the timezone challenges. This was brought up by a combination of market dynamics, internal pressure from employees looking to leverage LCOL areas to maximize personal gain, as well as a related shift in the job market overall based on the emergence of tech pockets like in the Netherlands (because real talent grows and eventually needs to grow teams to support their ongoing success). With this said, there are logistical challenges that prevent companies from being truly remote-from-anywhere (e.g. the need for tax entities in the countries where they hire) so there's still going to be some amount of magnetism towards specific tech-oriented locations (albeit better than Bay-Area-or-nothing).
As for real data: one of the most cited resources is the levels.fyi website. It's heavily skewed towards Bay Area, but you can also find information on other tech hubs, correlated to their respective gravitational pull for talent (e.g. Toronto, Canada has a pretty decent amount of data). Another thing to keep in mind is that job postings are often stale (sometimes by years) and they may be more open to remote than they seem.
Compensation is not equal everywhere, and a 200k bump isn't necessarily a given. It's more of a ballpark. The context is that a L5 role (roughly a 5-10 yr senior developer) pays a salary of USD ~150-200k/yr in the Bay Area. For comparison, a similar position for the same company in Bangalore might pay USD ~80k/yr, but Toronto might have very similar pay to the Bay Area pay range. Note that this is only the salary portion. A typical job offer from these companies usually also has an equity portion (i.e. stocks), and equity packages of 100-200k/yr are fairly normal in SV. Adding the salary and equity numbers plus a yearly bonus amount is typically referred to as "total compensation" (or TC) and is what these 300-400k numbers refer to.
In these conversations, typically we talk about L5 as the baseline because that's the level at which there are the most number of job openings for big tech, but there are also opportunities at L4 (junior level) as well as L6+ (staff level), with corresponding adjustments in pay. L6+ roles can in fact pay well north of 500k/yr TC, but needless to say, these are significantly harder to land roles, even in the Bay Area.
[0] https://www.youtube.com/watch?v=h8Xpapy6I9E