5 months and still a disaster

Please help me!

I started tackling sourdough 5 months ago after many years of baking chemical yeast bread. I bake on average 2 loaves per week. Generally I stick with three recipes on theperfectloaf.com (awesome website): the 50/50, Tartine #33, or all-purpose loaf. I obsessively read or watch videos about how to improve my bread and every time I think that I've finally figured out "my problem" I'm disappointed by the resulting loaf because the problem is still there (or a new one appears).

For a while I was making pretty descent loaves. They rose OK with an OK crumb and sometimes I even got ears. At the time I complained they weren't good enough. Now my loaves have devolved and they're like they were in the beginning: flat and dense with large holes. I'm at my wit's end about what direction to go because I thought I'd learned something about building strength, understanding how my starter works, etc. but it seems I've not learned anything at all.

In general I figured out that my starter is very fast. I can build a levain over night only if I put the levain outside in my garage (it's probably 10 degrees out there). Even in the fridge I have to feed my starter every 3 days. At room temp my starter is ripe within 4 hours. Generally I've stopped doing a cold ferment of my dough overnight as I thought it was over proofing so I've been doing a 7-hour cold ferment during they day and baking at night.

My loaf yesterday turned out flat, dense, with large holes. It was the 50/50 loaf from theperfectloaf. I had realised I had not been building enough strength into the dough so did slap/fold on the dough for 4 minutes initially. Then another set of slap/fold an hour later, and then stretch and folds every half hour for about 4 hours. When I shaped it for the cold ferment I thought it felt good and strong. After 7 hours in the fridge I took it out to bake. The dough had gotten a bit stuck to the towel despite flouring (this often happens to me..I don't understand why). As basically always happens, when I dumped the dough onto my baking pan it was flat and nothing like the pictures/videos I see of a dough that holds its structure. I don't understand why when I shape the loaf it feels good but after the ferment it's useless. Where am I going wrong?