1. I'm not against the idea of digital games but for me, it needs to be done in a way which makes sense for consumers. PCs definitely have an easier time getting this right, it's tougher for consoles since they often use different hardware although we're reaching a point where that's no longer a necessity so things could improve from here. Especially the DRM-free games stores on PC, where the game can be moved with no hassle to any new device people get and still played fine, that's the way to do it. Nintendo unfortunately has been the worst at things.
In my eyes, the advantage of digital should be that it's available in perpetuity, no worrying about something physical breaking, wearing out, or being stolen, and preferably not a worry about being unable to redownload it. Though, another problem I have is that digital games are effectively worthless. There's no way to get any amount of that money back. With physical I like the idea that I can make back some of the money sunk into all this junk, should I ever need it for whatever reason. Or just wanting to get rid of a game that ends up absolute garbage. Unfortunately setting up a way to sell digital games would probably be a logistical nightmare. Steam at least offers returns for a brief period of time, this is what all the shops should do.
Ideally both physical and digital should be offered to give choice, but since digital benefits corporations way too much, I don't expect physical to be around much longer.

2. I won't get into whether anyone really "owns" digital games, don't worry! This post is too long as it is and no one likes it when I flap my fingers like this! But uh, yes, to answer this question flatly, I have some digital games. I've never bought retail games as digital, though I have a few from promotions or something. Like when Nintendo offered some through Club Nintendo. 'Member that? Good times. A majority of the digital games I have were bought dirt cheap or plain free, because as I said above they're worthless to me so I treat them as such. I actually have over 140 on Switch due to its various fire sales, and about 30-40 or so each for Wii U and 3DS. All the digital games I have for Xbox are from Gold.
3. Yup! They're still often cheaper than digital thanks to retailer specials and the used market. Aside from stuff I mentioned above, space is also at a premium on Switch due to its dinky internal storage and only storage solution being microSD cards.
4. If it's physical I get physical. If it's digital I wait for dirt cheap or free. For Xbox, see number 5.
5. For Xbox I haven't bought any games, physical nor digital. I don't have any Series X discs, just the 7 Xbone discs my bro gave me, plus a host of 360 discs that I'm unsure are compatible. Instead... Xbox Game Pass! To cover the question first: Game Pass offers cloud gaming so streaming is an option for me, however so far I've only ever used it to complete the quests real quick. In those brief times I haven't had any issues, games load and play fine. I download the games I want to play, seems safer.
Since I treat digital games as worthless then I actually prefer the idea of a subscription service like Game Pass over buying individual digital games. I see no real value in "keeping" a digital game after I beat it, so rotating games in and out using a subscription just makes sense. It works out to be a much lower cost this way... especially since I don't pay for the subscription either! It's surprisingly easy to get free months of Game Pass through Microsoft Rewards, and while I s'pose it isn't "free" it hardly takes any time to get point and some go hand-in-hand with playing games so it goes full circle.
I know you only asked about specifically streaming and not a subscription service, but I figured I'd mention that I prefer a sub to streaming since downloading games is always gonna be more stable.