I am no expert, others will probably clarify with better answers.

Historically there used to be a arbitrary limit set: https://thebitcoinmanual.com/articles/wumbo-lightning-channels/

I think this number has been increased over time and may no longer be in place.

At quick glance 1,400,000,000 sats appears to be the largest so far (at least public) https://1ml.com/channel?order=capacity