So regarding a future transaction I should only take into account UTXO and not TXO right ?
UTXO is the bitcoin that you received and that you can spend.
Fees will be determined by UTXOs
Fee is determined by the UTXO counts. Assuming you send bitcoin to someone, and the UTXO count is 3 (I mean the transaction input is 3), that means you will pay more. But not only that, the more also the transaction output (the addresses you are sending to), the more the fee, but lesser in fee than to send each time to the addresses differently.
Any idea how minimum satoshis should a UTXO contain in order to be spendable so that fees don’t exceed the UTXO balance ? maybe fees in the future will be so high ?
Dust limit for legacy address is 546 sat. If it is native segwit, it is 294 sat. But why thinking about dust limit because the value is very small and not worth discussing. But some people use it for dust attack to trace certain transactions.