What guide are you following? I think “command not found” can be that it doesn’t find the file, or that it doesn’t find a library required for the file. When I check the OTP install guides, I see Fedora isn’t in the table of supported flavours, Installing on Linux using OTP releases - Akkoma Documentation
The “.” in the command refers to /opt/akkoma if you kept the defaults, so you might have to cd there before running the command or replace the “.” with the /opt/akkoma in the command.
Updating the path as advised before would also work.