It benefits China strategically and economically. Long term military wise, if Russia remains an active land mass threat to Europe, much of Europe and US will build a military for armed land conflict in Europe while leaving their strategic initiatives in the Pacific and Indian ocean underinvested leaving China to grow its power there. In the same way China is using Pakistan and the occasional skirmish in the useless high altitude Himalayas to keep India’s military focused on building a land-based military while leaving Indian ocean and its naval fleets underinvested.
There is a trend however, in several sectors: the financial volume of Chinese exports to Russia grows, but the unit volume does not.
That’s not called bankrolling, it’s called price gouging, and if someone price gouges an agressor, that’s actually pretty tolerable.
(I do not exclude that in other sectors, actual bankrolling may be occurring.)
Sources and background:
China Hikes Prices on Dual-Use Goods Exports to Russia – Study
China’s 2025 trade with Russia posts first decline in 5 years
China is successfully preparing Russia as a vassal state of China. Putin and Kim Jong-Un will be sitting next to each other as equals at the kids table at a meeting in China in the years ahead.