Experimento algo nuevo en verano.

In Spanish, seasons are often used without the definite article when referring to them in a general sense, so en verano is common. Saying en el verano isn't incorrect, but it sounds more specific and less commonly used in everyday speech. For example:
• En verano hace calor. (In summer, it’s hot.)
• En el verano de 2022 viajé a Madrid. (During the summer of 2022, I traveled to Madrid.)

Both experimentar and probar can mean “to try,” but they emphasize different nuances:
• Experimentar tends to mean “to experience,” “to undergo,” or “to test out something new.”
• Probar usually means “to try something out briefly,” often related to tasting food or trying on clothes.
In the sentence Experimento algo nuevo en verano, experimentar suggests that you’re exploring or testing something new in a more general or experiential way.

• Algo nuevo focuses on “something” singular and indefinite (an unspecified new thing).
• Algunas cosas nuevas broadens the scope to “some new things” (plural).
Choose algo nuevo if you have one specific experience or item in mind, or if you’re being vague about the quantity. Use algunas cosas nuevas if you clearly expect more than one new thing.