How to stop anxious barking in a dog that won't play?

We adopted a sweet little <2yo beagley-looking mutt in the spring. She's an absolute sweetheart (loves people, tolerates our toddler's silliness,) and after a few days of extreme reactivity to our cats, she was easily trained to get along with them wonderfully. Her issue is barking. Sometimes anxiously, sometimes just for funsies. I can tolerate it during the day. But she wakes up the whole house at night and cannot be calmed down. The obvious solution seems like it would be tiring her out more during the day, but she won't play. Throwing toys scares her. If you try to play tug-of-war, she just drops it. We got her a snuffle mat, and she'll use it, but she spends the whole time with her tail tucked, looking terrified that she's about to be yelled at, even when I pet her and encourage her while she uses it. And even when we take her to the park for hours, she still barks when we get home. She's great at digging, but she's only interested in digging out burrows, and even if I could provide her with an unlimited supply, I have to give her a bath afterwards, so it's not like we can make that her regular stimulation. She and our younger cat will make attempts to play with one another pretty frequently, but it'll only be a few seconds before one of them makes an interspecies faux pas and it fizzles. We've been doing a little training, but she gets so anxious, she has to leave the room and settle herself between commands. Everything I've read about building confidence seems to be based around exposure to people and new situations, which she's already fine with. I know barking is considered reactivity, but I guess I'm more asking about how to train her to enjoy any kind of activity that will tire her out so she's just such a bundle of nerves. Thanks for any advice y'all are able to give.