In Yoroi I can see that there is some ADA locked up with my native assets:
Can I spend this ADA without the native asset? If I would not care about the native asset, could I create a transaction that only spends the ADA and not the asset?
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In Cardano, each UTXO can contain a heterogeneous mixture of tokens and data, but must contain at least some amount of ADA. This is done on purpose to prevent both inadvertent and malicious chain bloat. Read more about the intricacies of minUTXOvalues here.
On your Yoroi wallet, you probably have a couple UTXO's with token data such that the min amount of ADA in each of those UTXO's totals to the locked amount displayed to you by Yoroi. In your case, it's not much, but if you want to free up the ADA you can always consolidate your assets into fewer UTXOs.
On Cardano you cannot transfer or own native assets (i.e. any token other than Ada) without having it combined with a certain amount of Ada. This amount of Ada is called the minimum Ada value needed and it depends on the byte size of the native tokens. Native tokens with large token names have a large byte size, those with small token names a small byte size. This constraint ensures that the total byte size of the ledger (all unspent funds of all wallets) has a maximum value and thus does not explode.
So, as long as you keep your native assets, you cannot spend the minimum Ada amount. Also, if you want to transfer your native assets in a simple transaction you need to send them together with this minimum Ada value.