Below error in dotnet core 8 can be solve by following below steps:

the name, or if a path was included, verify that the path is correct and try again.
At line:1 char:1
+ dotnet-ef
+ ~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (dotnet-ef:String) [], CommandNotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException

Step 1:
Configure the Package Source Mapping.
Path: Tools -> NuGet Package Manager -> Installed -< Right side(package source mapping found)

Step 2:
Open the Package Manager Console and run all these command one by one.
Path: Tools -> NuGet Package Manager -> Package Manage Console

Install-Package Microsoft.EntityFrameworkCore.Tools
Update-Package Microsoft.EntityFrameworkCore.Tools
Get-Help about_EntityFrameworkCore
No package updates are available from the current package source for project 'BearerAPI'.
Executing nuget actions took 0.03 ms
Time Elapsed: 00:00:02.1257780
PM> Get-Help about_EntityFrameworkCore

                     _/__
               ---==/    \
         ___  ___   |.    |
        | __|| __|  |  )   \
        | _| | _|   _/ |  //|\
        |___||_|       /   \/\

TOPIC
    about_EntityFrameworkCore

This get downloaded and upated.

I tried these commands:

dotnet-ef
dotnet tools install --global dotnet-ef