This was an excellent aerobic long run after the first quality week of the marathon block: 12.0 km at 7:05/km, with a very low average heart rate and comfortable sensations throughout.
The effort stayed exactly where it needed to be after the interval and fartlek sessions. Rather than becoming another test, the long run helped consolidate the week and protect recovery.
The mild fatigue you felt seems more like the usual discomfort of moving very slowly than real running fatigue. That is useful feedback: recovery runs should stay easy, but they should also feel smooth rather than forced or shuffled.
Takeaway. The first marathon-plan week was absorbed well. Keep protecting the easy and recovery days so the quality sessions can keep landing without accumulating unnecessary fatigue.
Next step. W02D2 Recovery Run. Gentle recovery running after the first full marathon-plan week. Keep it easy and smooth, without forcing an artificially slow shuffle.