So sorry about so much recent loss in your life! Can see how a pup with the spark of life, acceptance and ability to adopt to change can really be helpful to you.

Often older settled dogs that are sad, do not think of new interlopers as being part of the family too quickly. It takes time and they don't necessarily come to love on the young upstart at all. They don't think of puppies as we do as adorable and irresistible cuties. Sometimes it's more along the lines of 'that annoying pestering rodent that's shadowing us all'.

There isn't much information to go on regarding breed differences, size, and personality as well as age. But often very mature dogs are a bit put out by the energy of puppies.

Some breeds are a bit more maternal (including the males, eg the flock guardian breeds) and some will adopt the new kid and begin acting as a tolerant doting grandparent whose grandkid can do no harm -- but who greatly appreciates when the human 'parent' helps the older dog get needed space from time to time. After the upstart gets to be too spoiled on the 'grand'dog's terms, they being laying down the doggie rules.

Good luck!