I had a bike fit at Retul in Boulder a couple of years ago and they didn't mention that I had a discrepancy. I forget exactly how they measured it.
I got it in my head that I may have a leg length difference when I consistently noticed my left/right power imbalance. It took a concentrated pedaling effort, which felt unnatural, to even out the power balance. I put a cleat riser (not an angled shim) under my right cleat and had no change so I took it out.
I did some research and considered the posts above and came to the realization that the L/R balance doesn't matter for an amateur and that Shimano is aware, and has been for a while, about the balance issue in their crank-based, two-sided meters.
A confounding factor for me was that I have always had left, outside toe numbness and hot-foot. But never in my right toes/foot - only the left. I also have peripheral neuropathy in both lower legs, not diabetes related. I thus began a journey to see if I could fix the numbness and hot foot.
1) had the bike fit, including custom Specialized insoles (done in 2020)
2) shimmed my left cleat (done in 2020)
a) i use one glove size above my normal. for example i use extra large instead of large
b) i use one shoe size above my normal size
3) more recently shimmed my right cleat (2022)
4) tried and then removed my right cleat riser (again, not a angled shim) (2022)
5) moved both cleats to the rear as far as I could (2022)
6) just within the last week went from a 138mm saddle to a 155mm to a 165mm saddle (2022)
7) just within the last week moved my seat forward 15mm, yes I know that's a lot even though it's only about 6/10 of an inch, but I'm relatively older and don't yet have enough flexibility (2022). I've been off the bike for a year - some from laziness but almost six months due to a severe right calf injury unrelated to cycling
I may raise my saddle some to compensate for its move forward, just don't yet know how much to move it.
What clearly helped the most with outer toe numbness and hot foot in my left foot was moving the cleats completely to the rear. Second best was shimming the left cleat and the bike fit. That's where the left shim came from. The fit mostly took weight off my hands.
I did 18 miles last night with all the above in place. Problems largely resolved even though it's a sample size of one.
Next on the list of things to try if the above don't continue to work include:
https://mid-foot-cycling.com/
https://www.g8performance.com/insole...ievers-bundle/
I do not have any affiliation to any product mentioned in this post.
Glenn