With every halving, assuming price remains constant, BTC miner revenue, and with it, energy expenditure, declines, until it's 10% of current energy expenditure.
You're right that this could pose problems for Bitcoin's security, but that's unrelated to the fact that Bitcoin miners' energy expenditure as a share of BTC price will decline.
It’s nowhere near consistent enough to say 10% going forward, as block rewards per day have been anything from 1400 to 10 BTC per day over the last 3 years.
https://www.blockchain.com/charts/miners-revenue
With every halving, assuming price remains constant, BTC miner revenue, and with it, energy expenditure, declines, until it's 10% of current energy expenditure.
You're right that this could pose problems for Bitcoin's security, but that's unrelated to the fact that Bitcoin miners' energy expenditure as a share of BTC price will decline.