Hi @alex , I faced similar issue when tried creating it through Azure Portal in East US region but worked fine with North Europe region. Also was able to do it with Azure CLI. Below is the command I used.
az mysql flexible-server create --location northeurope --resource-group xxxxxx --name xxxxxxx --admin-user xxxxxx \
--admin-password xxxxxx --sku-name Standard_D2ds_v4 --tier GeneralPurpose --public-access 0.0.0.0 \
--storage-size 32 --tags "key=value" --version 5.7
Can you please try this once and see if it works in other regions?
For the Azure Portal issue related to few regions I have escalated it to product group and will update here as soon as I get a reply back.