It looks like a leaf spot disease which could be bacterial, fungal or even viral. Either way, those generally only affect plants which are already stressed, perhaps due to being short of water or nutrients, both of which are likely in a potted camelia. You could first try cutting off all of the infected leaves (just in case they are infecting leaves below) then watering it well for a few weeks and seeing if the new leaves and shoots are 'clean'. If ok, I would then feed it with an ericaceous plant feed. Camellias need ericaceous soil so make sure you use a loam-based ericaceous compost if repotting it.
A trowel in the hand is worth a thousand lost under a bush.
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The following link should help with advice for you.
(Make sure you maintain good hygiene around the plant and clear any fallen leaves)
https://www.rhs.org.uk/advice/garden-health/problems/Camellia-problems-frequently-asked-questions
That has a bearing too
I live in west central Scotland - not where that photo is...
Best not in early morning sun. They like shade, my best ones are in shade.
But what causes the leaf problem?