In the UK, what often is described in the US as a “2x4” is, technically, 38x89 - it’s 2"x4" before finishing, and ends up smaller in terms of actual dimensions.
I can find similar in the UK as ‘stud timber’, often described as ‘CLS’ for “Candian Lumber Standard”, as the type of softwood. Eg, like this. Any timber used for framing would do.
Hardware stores are not nearly so diverse in Europe - lots of what the US Youtubers will pick up in a Home Depot we have to go to more specialist places. Lumber yards, even ones aimed at builders, will perhaps be a better bet for timber, and finding my country’s specialist woodworking places is great for finishes.
Some finishes don’t exist in Europe because of chemical restrictions, but not many. Polyurethane varnishes and danish oil should be findable for sure. Osmo make lots of great stains, oils, and waxes, for instance - try searching around for a place that will stock them, because if they do, they will have the rest. Again, though, my local hardware stores have crap selections, and it’s off to Axminster or similar (a specialist tools/woodworking store, who I buy from online) for Actual Stuff For Woodworkers.
I don’t know PT specifics, but I feel like this stuff must be available. The problem is finding the thread of where it’s stocked. So I’m just trying to suggest ways in.