Unless you like being a traffic jam I’d try and stick to one side of the Lakes or the other, basically Keswick area or the Ambleside/Coniston area.
I’m from the South Lakes so might be biased 😆
The Elterwater/Iron Keld loop is decent and pretty much all-weather, doesn’t go high either plus you can shorten it or lengthen it according to time/whim.
There’s quite a bit in Grizedale Forest that isn’t trail centre stuff: from the centre do the TNF climb then head over to Parkamoor, don’t descend to Nibthwaite (though that’s a good descent) but cut back in to the forest and do the Grandfather, Father, son descent (I think it’s called that, check on Strava) o Satterthwaite then either cut back along the road or head up the other side and there’s a trail or two there but don’t know what they are called.
Staveley – Green Quarter – Selside – Kentmere – Three Rivers – Staveley would be another good loop. Also from Staveley you can head towards Troutbeck then back over Garburn Pass and back via Three Rivers.