I’m not aware that staking to multiple pools is supported in Yoroi. It’s not supported in Daedalus simply because the feature has not been added. IOG are focussing their attention on developing Lace which does support multi pool delegation.
To use a different wallet interface with different features you can simply use your seed phrase or hardware wallet to restore your wallet.
The “ONE wallet” you are mentioning is not one wallet. " Create new wallets" and " Add additional accounts under the same wallet" means creating new wallets, either by using a new seed phrase or by using the same seed phrase, but a different derivation path. The funds you have in the different wallets can only be managed (and delegated) in those wallets. They are completely independent.
The multi-delegation for one wallet in Lace is done by using multiple stake keys for one wallet and splitting the funds between payment addresses created using the same payment key and the different stake keys, and by rebalancing the funds between those addresses on each transaction, so that the proportion of ADA on each address is constant.
Development of Daedalus was very slow for months and years.
And for good reasons: There are not that many users of Daedalus left. The resource usage makes it infeasible for a lot of people and there is no really good reason to invest those resources. It helps neither the user nor the network.
Attention of IOG has quite completely shifted to Lace. And there have been other great browser-based wallet apps for quite some time. If there is no very good reason to use Daedalus, use them.
(If Lace’s multi-delegation gains traction, they will likely come up with alternatives. Delegation to multiple pools with several accounts is already almost the same, would just need automatic rebalancing functionality.)
If your reason for using Daedalus is security, please consider using a hardware wallet instead.
Daedalus does not have significantly improved security due to being a full-node wallet. It still stores your secrets on the computer encrypted by the spending passwords exactly like all the browser-based wallet apps do it. Malware can get at that almost as easily. The only small security benefit is maybe that it is a stand-alone application which makes scamming users with a fake wallet app harder and potentially excludes some vulnerabilities of browser storage (although those are not really the weak points of browsers as far as I can see).