I've recently been thinking of ways to make elderly parents feel less lonely during the day, or in between visits and calls.
If your parents are experiencing this as well, I would love to have a quick chat with you to understand what their day usually looks like, what you've tried so far and where they are having the most issue.
You can hire a companion aide to come to the house and spend time with them, take them out for a walk, play a game or just chat. Some churches may have volunteers who will do this.
If the parent is able to leave the home, you can look into Adult Day Care. Often, they will send transportation to pick up the elder and bring them home again. Social interaction and activities are available for those who want that.
Remember that not everyone has the same idea of "lonely" and not everyone relishes social interaction. I'm speaking as an introvert. I used to wonder why friends and neighbors would always try and push me to do things that they liked to do. I felt pressured, and guilty saying "no". It took me a while to recognize that some people are energized by social activity, while others, like me, feel drained by it. So, don't push anyone into something they have no interest in doing. Joining a group of others for crafts and games would be torture for me.
One thing I suggest is to resist becoming your parents' Entertainment Committee. If they can't figure out how to keep themselves and their minds occupied at least some of the time, then you're going to be orbiting around them endlessly (and it may be a sign of cognitive decline/impairment and they won't be entertained because their brains are broken). It will burn you out.
That being said, I think technology can fill a lot of those hours. Many years ago I gave my Mom my old iPad and loaded games on it. She uses it every day to entertain herself, plus watches animal shows on tv. She's 97 now and lives next door to me and I have to have boundaries about not being her solution for entertainment or else I'd never get anything done (she has mild/moderate dementia/memory impairment). My Mom also still cleans her house, takes care of her own hygiene (mostly), can still prep some of her meals, gardens a little. And that fills up a lot of each day. If your parents aren't doing any of this, then maybe there's a different problem that needs to be solved.
If you're seeking ideas for your own personal implementation, then all of those can be posted here in the thread by other participants. That's how this forum works.