The ability to cast at least one spell
Through innate connection or intentional effort and focus, your magic has specialized in one element or theme far more than the average spellcaster. Your skill and knowledge grant you access to spells unreachable by those who merely dabble in those types of spells.
You gain access to one of the spell lists below. However, not all the spells may be castable by your class. Spells that cannot be cast by your class can be cast using spell scrolls. When using a spell scroll of a spell from your thematic spell list, you treat that spell as though it were from your class's spell list, regardless of whether it actually is. For spell scrolls for spells of a higher level than you can cast, you can add your proficiency bonus again to the ability check you make to cast it.
Aeromancy
Acidomancy
Cryomancy
Hemomancy
Hydromancy
Geomancy
Lumomancy
Pyromancy
Tempestarii Magic
Toxomancy/Poison Magic
When you acquire your thematic spell list, you can swap out a number of spells, cantrips included, equal to your spellcasting ability modifier (minimum of 1).
You can take this feat multiple times, choosing a different theme each time.
This feat could be gained in place of an ASI like normal or can be acquired through a quest, as a result of effort spent during downtime, or through some other method. Please talk to your DM about how you develop your Thematic Magic.