Consider the scenario - a wizard is in melee with individuals who will opportunity attack the wizard
the wizard walks away triggering the opportunity attack and then casts shield to prevent damage
as The Wizard moves away they use their action on their turn to cast burning hands on the enemies
Are the players allowed to cast reaction spells on their turn, the wording in the players handbook is still annoyingly vague
Casting Time
Most spells require the Magic action to cast, but some spells require a Bonus Action, a Reaction, or 1 minute or more. A spell’s Casting Time entry specifies which of those is required.
One Spell with a Spell Slot per Turn
On a turn, you can expend only one spell slot to cast a spell. This rule means you can’t, for example, cast a spell with a spell slot using the Magic action and another one using a Bonus Action on the same turn.
Reaction and Bonus Action Triggers
A spell that has a casting time of a Reaction is cast in response to a trigger that is defined in the spell’s Casting Time entry. Some spells that have a casting time of a Bonus Action are also cast in response to a trigger defined in the spell.'
I wish they would just say yes/no you can/not cast a reaction spell on your turn and another spell as either a bonus action or an action
in the example you gave, the wizard who walked away would be able to cast shield as a reaction on their turn. If they have already used a spell slot to cast a spell on their turn, then they could not cast shield on their turn. And after a casting shield on their turn, they could not use a spell slot to cast a spell for the rest of their turn.
On a turn, you can expend only one spell slot to cast a spell. [...]
You could if one of them were a cantrip or because it's a spell you can cast through traits/features/feats that grant characters prepared spells they can cast without using spell slots.
Consider the scenario - a wizard is in melee with individuals who will opportunity attack the wizard
the wizard walks away triggering the opportunity attack and then casts shield to prevent damage
as The Wizard moves away they use their action on their turn to cast burning hands on the enemies
Are the players allowed to cast reaction spells on their turn, the wording in the players handbook is still annoyingly vague
Casting Time
Most spells require the Magic action to cast, but some spells require a Bonus Action, a Reaction, or 1 minute or more. A spell’s Casting Time entry specifies which of those is required.
One Spell with a Spell Slot per Turn
On a turn, you can expend only one spell slot to cast a spell. This rule means you can’t, for example, cast a spell with a spell slot using the Magic action and another one using a Bonus Action on the same turn.
Reaction and Bonus Action Triggers
A spell that has a casting time of a Reaction is cast in response to a trigger that is defined in the spell’s Casting Time entry. Some spells that have a casting time of a Bonus Action are also cast in response to a trigger defined in the spell.'
I wish they would just say yes/no you can/not cast a reaction spell on your turn and another spell as either a bonus action or an action
in the example you gave, the wizard who walked away would be able to cast shield as a reaction on their turn. If they have already used a spell slot to cast a spell on their turn, then they could not cast shield on their turn. And after a casting shield on their turn, they could not use a spell slot to cast a spell for the rest of their turn.
"Not all those who wander are lost"
If we're using the 2024 rules, you couldn't cast both spells in the same turn: One Spell with a Spell Slot per Turn.
You could if one of them were a cantrip or because it's a spell you can cast through traits/features/feats that grant characters prepared spells they can cast without using spell slots.
EDIT: I got ninja'd by @TexasDevin!
Brilliant thank you everyone