I believe there is a bug in this mod because I am unable to pick up lava from cauldrons. It's intuitive that buckets should be able to pick up lava from cauldrons just like they can from regular lava source.

It would also be cool if big buckets could be inserted as fuel in furnaces.

Are you on fabric or forge?

I'm on fabric 1.19

Thanks. Also, does it not work with water cauldrons either?

The big bucket (of any size) won't interact with any fluids inside a cauldron.

Thank you. I'll look into this.