Storage is cheap, especially at the corporate scale.
Make two simplifying assumptions: pretend that Google is paying consumer prices for storage, and pretend that Google doesn't need to worry about data redundancy. In truth Google will pay a lot less than consumer prices, but they'll also need more than 1 byte of storage for each byte of data they have, so for the sake of envelope math we can just pretend they cancel out.
Western Digital sells a 22TB HDD for $400. Seagate has a 20TB HDD for $310. I don't like Seagate but I do like round numbers, so for simplicity we'll call it $300 for 20TB. This works out to $15/TB. According to wikipedia, Youtube had just under $29b of revenue in 2021. If youtube spend just $100m of that — 0.34% — they'd be able to buy 6,666,666 of those hard drives. In a single year. That's 6,666,666x20TB = 133,333,333 TB of storage, also known as 133^note^ ^1^ exabytes.
That's a lot of storage. A quick search tells me that youtube's compression for 4k/25fps is 45Mbps, which is about 5.5 megabytes/s. That's 768,722 years of 4k video content. All paid for with 0.34% of youtube's annual revenue.
Note 1: Note that I am using SI units here. If you want to use 1024^n^ for data names, then the SI prefixes aren't correct. It'd be 115 exbibytes instead.
EDIT: I initially did the price wrong, fixed now.