Hi,
Dedicated Hosts typically cost thousands of dollars per month. Are you sure you want to practice with one?
You need to increase vCPU Quota for the instance family and region you would like to create the dedicated host in. The amount you need depends on the specific size and region.
In the screenshot you are choosing Standard DSv3 Family - Type 3, which has 80 vCPUs for each host, so you need at least 80 vCPUs available for that instance family size and for Total regional vCPUs for the region you choose.
In your example you only have 10 vCPU quota for that instance family remaining, so you would need 70 additional vCPU quota for the instance family plus increase the Total Regional vCPUs for the region you are creating it in.
You may navigate to Quotas in Azure portal and request what you need:
https://portal.azure.com/#view/Microsoft_Azure_Capacity/QuotaMenuBlade/~/myQuotas
IMPORTANT: Dedicated hosts typically cost thousands of dollars per month. As a result people don't use them for practice in my experience. If you still want to create one understand you need to delete it immediately afterwards so that charges do not continue to accrue.
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP