It depends.
In regards to your 2019 tax return that you mailed in, the IRS processing centers are not open due to the social distancing and therefore, are not being processed at this time. They will be processed once the IRS centers are allowed to reopen.
IRS operations
In regards to your stimulus payment, the IRS will probably issue your payment if you meet all of the requirements based off your 2018 tax return as filed since they have not processed your 2019 paper filed return.
The following links can also be used for additional information.
TurboTax Corona Virus Tax Center Updates
IRS Coronavirus Tax Relief