hi OP, I'm in a similar situation in that I am a LP who has my DD 100% of the time, no family nearby to help and because of the situation I can't build a social life, old friends have dropped away.
It is really tough, and ignore the PP who said that you should get enough from your kids alone! You have social needs that can't be met through doing childcare or being a mother.
the ways I deal with it are working on a self employed business during the evenings, having a structured day with regular habits, daily exercise at home etc. Somehow the routine gives me a structure that makes the loneliness bearable. Social stuff has to be done when the kids are at school, maybe book yourself in part time course or something, even if it's done on zoom. You need time out of the house - even if it is with the kids - regularly on a weekly basis like one outing a week or even just a trip to the park / shops.
As PP has suggested podcasts are really great - I find self help ones focussed on loneliness or self improvement, single parenting etc to be a real support.
Regular calls with family and old friends when you can. Career can be important and an important distraction - even if you don't have a full time job, something you can focus on in the evenings eg. start a blog / set up a small craft business / social media page or something fun for you to focus on.
Sometimes the only way is through, you can do everything to try to make new friends but remember it won't last forever and try not to get disheartened if you can't maintain it - try to make your situation the new "normal".
Find a few good sitcoms or tv shows you look forwards to each evening.
Finally I think in some ways we have to reframe the loneliness - think of it as a large amount of time you now have to focus on yourself / your personal development / your interests etc in the evenings. What part of your personality are you going to grow, what new hobbies can you do, what yoga can you do in the eve to improve your health etc etc. It's not perfect but it is a gift in that sense and you might find these things more fulfilling ultimately, because you are doing something really meaningful to help you develop.
Eventually you will have free time again!