Does the new episode work well in opensource ports? (don't feel like installing steam rn and don't care about nightdive port)

The modding changes mentioned at the bottom of TFA seem to imply that text strings won't render properly until the source ports are updated. You're going to have to install the NightDive port anyway to download the new episode. I don't think they have a separate download for it. I'd imagine everything else might work okay already or will be fixed alongside the string issues.

They need changes to support it, but I don't expect it to take long. Both vkQuake and IronWail work well with the previous new official episode (Dimension of the Machine) and the remastered models after they were updated for that.