The current minimum amount of Bitcoin that you can send in a single withdrawal from your Swan Bitcoin account is 0.0001 Bitcoin (10,000 satoshis). This is roughly a single-digit dollar amount at mid-2021 prices. We have chosen to include a minimum withdrawal limit because withdrawing Bitcoin in small chunks creates a future problem for you to spend it.
Bitcoin costs more to spend when more small chunks (called UTXOs) must be "smelted together" in a single transaction. For example, it will cost more to spend 0.1BTC that you received as ten separate 0.01BTC withdrawals than it does to spend 0.1BTC that you received as a single withdrawal transaction. Think of it like handing someone a $100 bill vs handing them the same amount as ten thousand pennies.
Bitcoin transaction fees are proportional to the "weight" of the transaction, or roughly the count of the different chunks, rather than the amount you're sending. Thus, keeping your Bitcoin in larger chunks may be beneficial to your future ability to spend it. As Bitcoin fees are predicted to rise in the future, it is to your advantage to avoid small chunks of Bitcoin that could turn into unspendable Bitcoin dust.
Automatic withdrawal plans on Swan are gated to a once per week withdrawal for the same reasons. If you want to withdraw sooner than that, you can use Manual withdrawals. However, please consider chunking your Bitcoin to reduce your future transaction fees.
There is no maximum withdrawal size. You can withdraw as much as you'd like.