On the BSC or ETH chain, what is the maximum total supply I can set when creating a token?

This is a great question. Here’s the conclusion:
If your token’s decimals (precision) are set to 1, then the maximum total supply you can set is:

10,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000
(that is, a 1 followed by 76 zeros).

Of course, for each additional decimal place, you remove one zero.
If you use the default 18 decimals, then the maximum total supply is a 1 followed by 58 zeros.

So yes — setting your total supply to 10 quadrillion (or even much more) is absolutely fine.