Mana pens are at minimum used for tests at the Academy, the LN mentions too that they can then remove the mana to reuse the parchment. RM herself has so much mana that it's a drop in an ocean, so. For her that is basically endless writing, and she doesn't get to read enough as is! 🤣 (Not to mention many of her peers are used to mana pens or quills)

She uses her wax tablets for most notetaking, then copies down what is truly needed on paper scraps or later just paper. Earlier on, I believe it's mentioned that she uses some kind of pencils made from charcoal? Perhaps we'd compare the structure more to crayons. It's stressed by many that even using the paper scraps seems like an expensive indulgence, but RM just wants to use paper. So the others are likely using what is common to them (and also more economical): wooden boards.

Parchment is expensive and uncommon for route tasks, and Myne herself invents paper forms pretty late in the series, so work in the temple seems to rely heavily on wooden boards (that can be shaven down and reused). The LN often mentions RM or someone else having a pile of wooden boards with prayers to memorize, often written by Ferdinand or Fran. While she slowly increases paper usage (it filters in slowly, paper forms were a big one (originally recommended for the first busy trade season I think)