@Peaceful I think the reason so many of the streams around Hood and Portland close because they represent a perfect storm of factors -- the trout are spawning, anadromous fish are returning to spawn, they're close to a major metro area and most of them flow on public, easily accessible property. I do wish they'd be a bit more nuanced about which close and which are open. I don't think the Zig Zag would get overfished in the winter, it's not like the weather up there is great. A river like the East Fork Hood, on the other hand, should be closed because winter is the only time there's any visibility and locals would hammer it.
Systems to the west, like the Yamhill and its tributaries, I've always assumed they're open all year because ODFW can't reasonably pretend recreational fishing is the issue for fish populations in and around that much private property and farm land. They're essentially saying, "Sure, come fish year-round in a lost cause." They're also hard to access and have a short season, their low altitude makes them susceptible to blow out in the winter/spring and they get low quickly in the summer. And as a general rule, if a local stream is open for trout year-round, you're in tweakerville. I've spent the better part of the last two years on this same quest and I definitely understand your frustration/general discomfort with the parking situation.
In my experience, winter fishing in Oregon divides roughly into two chunks -- November - January and then February - April. I know April isn't technically winter, but it is at altitude, and altitude matters more than May 23 when it comes to good trout fishing close to Portland.
That first chunk is just rough, it's rainy, the weather is inconsistent, the flows are all over the place and in my opinion there just isn't anywhere within 90 minutes of Portland worth your time. The Lower Deschutes and Middle Fork Willamette are 2 and 2.25 hours from Portland, respectively, and they're so easy to access that the extra drive time is more than made up for by how quickly your bugs are in the water. Same goes for the Crooked. It's a lot of driving, but it's also a lot of fishing. Hard to say the same for a day spent looking for bridge easements on Gales, or wading through cow pies on the Yamhill.
In February, ODFW starts stocking low elevation lakes, like Hagg. Hagg is also worth fishing in December and January if weather allows, there are holdover rainbows and wild cutthroat in there, and you can fish all of the creeks that flow into the reservoir. The fish in those creeks are very small, but beautiful, and so is the scenery. You also don't have to worry about private property since it's in the middle of a park. Benson and Blue Lakes are also stocked starting in February and early March, but those lakes are entirely dependent on the stocking truck and with ODFW's schedule still offline, it'll be a guessing game. Blue Lake is about 15 minutes from Portland and has a fairly suburban park feel, Benson is a bit prettier, right next to Multnomah Falls. It's loud (the freeway is right there) and gets windy, but it's a fun place to hone your craft if still water fly fishing is new to you.
And depending on when the snow melts (and how badly the fires damaged the road in), Lake Harriet should be an option sometime in March or early April. It's about 90 minutes. Around that time, you might also consider hiking into Trillium, Mirror or Frog Lakes to see if they've thawed. After ice-off is one of the best times to fish the lakes up on Hood.
In general I can't stress enough how worth the effort is to perfect your still water techniques if you're a Portland fly fisher. The low elevation lakes will be an option months before the general trout season opens on the small streams, but that ends up being a footnote to the lake fishing in spring, summer and fall. If you fish the Zig Zag or Upper Clack all day for a week, you might get a fish a day over 10 inches and find one over 14 if you're incredibly lucky. The lakes hold trophy fish. They're a blast. I love small stream fishing more than anything, and had zero interest in still water when I moved to Portland. Now I spend my entire May and June and most of October ignoring them to fish lakes. The best part is that they're by far the closest options, too. You can be at Trillium or Frog Lake in an hour, Laurance or Harriet in an hour and a half, Lost Lake (the one on Hood, not the coast) 15 minutes further. Most of them are stocked, but all of them also hold self-sustaining populations of wild and native fish. You can catch wild cutthroat, brown, rainbow, brook and bull trout by visiting as few as two of them.
Side note, I noticed someone mentioned Tanner Creek above, but it's not open year-round. And sadly this year it was inaccessible, the trail that follows it is the same as a very popular hike that was closed off all year due to COVID. I have heard it's a fun fishery when it's open. It flows into the Columbia near Bonneville Dam, so it's well within an hour of Portland as well.