Fact - you can use thicker oil without issue.
Fact - navigating information on this topic is too complicated for most people - so you should just follow the Subaru owners manual.
Problem - There's zero consensus and it's mostly opinion. Unlike 'engine rebuild' and 'transmission rebuild' and highly technical questions which generate replies with compelling insight....not so with oil - anyone and everyone comments.
What you want is to hear from the best of the best - but they're simply not easily available. (high capacity people rarely spend gobs of time discussing easy mundane things like this - they're actually building, creating, and leading the way forward). So you won't hear from guys that are incredibly valuable in their experience, backgrounds, and capacity to talk quantitatively about this stuff rather than just regurgitate whatever fits their suspicion/desire. Here's two of them that repair/build engines better than Subaru and beat the average by an order of magnitude, and can talk about practical platform specific Subaru information better than almost every one. I've spoken with these guys and they are incredibly sharp and got there by extensive high capacity learning and attention to detail from any angle - not taking stands:
Ivan'simports in Canada
Owner of this place:
https://www.facebook.com/superiorsoobie/
There's more, but the top notch folks are rare. What you'll get from this forum is woefully short of what they could teach on this subject. These guys have learned their views, not just staked them out on preconceived notions or the unicorns of "subaru engineers" et.al.
Ideally you learn from guys like that - but that's highly unlikely - so stick with the owners manual.
"Subaru engineers" - The magical wizards that have added additional failure modes that never previously existed in Subaru's: EJ25D piston protruding headgasket blowing, Phase II headgasket weeping, rear separator bleeding, wheel bearing eating, caliper pin bushing seizing, low grade head repair non-resurfacing, FB oil control ring consuming, EZ engine internal HG failing....and more...
I totally get it - there's so much information who do you trust? best to trust Subaru, that's a great starting point and due to the issues outlined above - probably needs to be the end point for most people.
So follow Subaru. But there is a more compelling and robust take on "oil topics" than what you typically hear and read about online. By and large oil choices are way over played and magnified. Everyone thinks they're awesome because they got 200,000 miles on XYZ....when in reality that's just normal and eveyrone else that doesn't even care about cars drives 200,000 miles on whatever oil is on sale.
I just prefer a complete and accurate picture of what's going on - even if it means the OP lands in the same boat - follow the owners manual.
I'm still waiting for evidence of any engine failure or early demise of any modern engine, made by any manufacturer, caused by the use of 0-20 oil.
I think lack of oil is the main issue, not weight. Could that same statement be applied to those running heavier weight oils? No issues there either.
But either way - control rings are the issue so oil choice is probably a cheap band aid at best?