Temper tantrums?

Not completely ignore, but don't get involved either. I keep a neutral face, and try not to talk - if I do feel the need to speak, I talk very very softly, barely a whisper. Just be calmness. I don't offer comfort until it starts passing or she reaches out - not to be unkind, I just don't think it's helpful. I am ND and I sometimes have meltdowns that are very similar to tantrums and actually the best response my partner can do is to be soft, calm and wait it out - anything else ramps the energy up higher. Toddlers cannot regulate their emotions yet (and I struggle to when I'm in crisis so I understand!) And these tantrums are an expression of their intense feelings. But your calm is their calm.
It won't work overnight. Growing up takes a long time.

Ignoring = cold. I would say what I do is warmly waiting.

It's ok for them to be upset! That's what I try to remind myself. They're allowed to be upset about a boundary I've set, but that doesn't mean the boundary changes. I usually just try to stay available while also not adding fuel to the fire by trying to fix the tantrum or dismiss his feelings. It's easier said than done, I know. Sometimes singing a song is enough to distract my son, sometimes he just needs to feel his feelings and that's ok too. For example one of our rules is no toys at the table when we're eating, so this morning I had to put my son's toy away before breakfast and he got upset. He was sitting in his high chair and just screamed and cried but I just calmly moved on to the next thing (eating my own breakfast) until he calmed down enough for me to offer him his food. It took a while but eventually he calmed down and ate. I think the difference between ignoring and calmly being available is having open body language and keeping a neutral expression rather than turning your body away from them

Oh it’s so difficult isn’t it. My son is 18 months on Monday and the tantrums that have come on these past couple of weeks have been so difficult. I’m very gentle with him, sit and wait, or I continue with what I need to do and keep checking in to see if he wants my attention or if my redirection works. It’s been a learning curve for me and him, and each tantrum im trying to get better at managing. I think it’s a case of just riding out. I always try to remind myself that the big emotions they’re feeling are soooo intense, and it must be really confusing. Breathers for myself and trying to ground/regulate myself throughout is a must. Eventually they will settle, we’ve just got to ride it out with them. Sending lots of love, hugs and prayers to you🤣

I’m going through the same right now with my son, I try my hardest not get frustrated by not and I pick him up and hug him and tell him it’ll be okay he works sometime but other days it’s a struggle

I could have written this. I have such a chilled, happy little girl but this Christmas period, she's turned into a right gremlin. The public tantrums are the worst as I can't do a lot but carry her around until I find a distraction. I'm so glad it's not just my LO. I honestly thought we'd gone wrong somewhere...