@IT 一郎 Thanks for your patience on this, our engineering team has investigated and confirmed that this is a known issue in free trail subscriptions while creating the standard logic app from portal you won't be able to select the storage account and currently, we don't have any ETA for this once we have any updates I will update you here.
A temporary workaround is to try creating the logic app using Azure CLI cmdlet az logicapp create
instead of using portal.
Feel free to reach back to me if you have any questions on this.