There is via Battlenet Tokens you can buy in game for gold, or through a re-occuring subscription.
Bnet balance has never been available for use on a Sub. Just for game time blocks. The game A few years ago they also removed the single month, 3 month, and 6 month game time blocks. They only offer 2 months now.
Those changes were made in March of 2021.
I made up a handy chart at the time to help people see their WoW payment options at a glance. Note that any taxes and fees mandated by law in your state/country are additional.
| Description | Cost (USD) | CC | PayPal | Debit | Bnet Bal | WoW Token | |
|---|---|---|---|---|---|---|---|
 |
1 Month reoccurring Subscription* | $14.99 | X | X | X | ||
 |
3 Month reoccurring Subscription* | $41.97 | X | X | X | ||
 |
6 Month reoccurring Subscription* | $77.94 | X | X | X | ||
 |
1 Year reoccurring Subscription* | $155.88 | X | X | X | ||
 |
WoW 30 day game time token (with gold) | Gold | |||||
 |
60 day Game Time Card/Block | $29.99 | X | X | X | X | |
 |
Battlenet Balance (your account)** | Flex | X | X | X | X | |
 |
Gifted Battlenet Balance | Flex | X | X | X | ||
*If you don’t want your Subscription to automatically renew, wait for it to clear the payment (several days), then cancel the Sub on the account. You can do this every month if you like.
**Check the Bnet Balance article for Restrictions and use https://us.battle.net/support/en/article/25904