Did you mean I cannot spend multiple transactions at once?
You're never spending multiple transactions, you are spending multiple transaction outputs. It is possible and easy to do so. Just reference all of them in the transaction that you want.
Can you please explain more? So If the wallet has 1 btc that was received in a multiple unspent transactions. e.g. 10x 0.1 BTC deposited. Then I want to spend them all, which transaction should I use its TXID now?
All of them. The transaction needs to reference all of their TXIDs and their corresponding indexes.