Welcome to the forums. The frame has some interesting characteristics. The workmanship is indicative of a production built frame but the serial number format looks like yy mm xx, which would typically be a small builder. The 26.8mm post indicates a medium to high grade tubeset. It has a short rear dropout with derailleur hanger and brazed-on shifter bosses and bottle mounts but not top tube cable tunnels. The front brake uses a recessed bolt but the rear doesn't. Derailleur cables are routed over the BB shell. The component mix is wide ranging, both in terms of age and quality. It has obviously been repainted and rebuilt with many non-OEM components and possibly even additional braze-ons, all which complicates identification. My overall impression is a very late 1970s, mid-range model.

As to the manufacturer, my initial thoughts were Motobecane, based on the style of the stay caps but the tubing isn't metric, based on the post size. Most of the Scandanavian market bicycles that we see comply with the Danish Bicycle VIN System. Consequently, this would be my next step in the identification process. Typically this number is stamped on the seat or down tube and will tell you both the manufacturer and year. Good luck.

https://en.wikipedia.org/wiki/Danish_bicycle_VIN-system