Sorry you are struggling op. If it’s any consolation, I don’t think you are the only one!
I have lived abroad for various parts of my life in different EU countries and the number of my friends who returned home to Ireland after their posting and struggled once they got there, for the same reasons you mention, is significant. Quite a few moved away again back to an expat situation.
And I say this as someone who absolutely loves Ireland and comes from a half Irish family.
To be fair, I don’t think this is exclusive to Ireland either but just particular locations with tight knit communities where people still have families around them, and where friends grew up together and stayed together. So much so they are not really looking to make new friends.
If you have tried the usual hobby groups, volunteering and it hasn’t work, are you at liberty to move somewhere else?
If moving isn’t possible then another solution if you are rural, and you can afford it, is to buy an animal or two and attend events and shows and get to know people that way. It could be rabbits, hens, dogs, ponies, cows, sheep. It doesn’t matter. Just as long as you can pursue a few activities with them. I think animals always bring good people in to your life.
Or, as you can’t be the only person in a similar situation, it’s a bit of a risk but could try making some mince pies and advertise on local sm and open your doors to anyone who is alone on one day of Christmas week? Maybe an event where people contribute a very small amount which you then give to a charity? But you might get to know some nice people at the same time? It only takes one or two. And if you hold it next week, it will be those who aren’t frantic with family stuff who might attend?
Last suggestion is to form a book club/quilters club/walking group/board game club, and you be in charge of the organising and hosting either at your home or in a local pub, and that way you get people’s phone numbers. And then after a while of getting to know people once a month, you can invite a few out individually?
Good luck 💐