If you are looking for non-technical options then heading up to the summits in the North Lakes is probably not advisable really.
Loughrigg is a good call, sticking to the bridleways will offer no challenges but still be more interesting than a trail centre red. I would look at expanding it to take in Iron Keld too, via Little Langdale.
Walna is a mountain pass, albeit one without huge elevation. It’s been sanitised so much nowadays that the descent to Coniston would be doable on a gravel bike.Again, if you’re after something good but not too technical, then it’s a good option if you fancy a larger ride.
Other options would be Claife/Grizedale, Ullswater Singletrack, Kentmere (although Garburn Pass is definitely not trail centre red).