The 27-year-old Spanish under-21 international – who won the European U21 Championship with his country in 2019 – spent last season on loan at the Andalucian club, where he made 26 appearances.
Roca joined in the summer of 2022 from Bundesliga giants Bayern Munich in a £10m deal.
He featured 36 times in all competitions in a mixed 2022-23 campaign which ended in United being relegated from the Premier League.
Betis exercised Roca’s relegation release clause last summer.
Roca was two years into a four-year deal at Elland Road.
Sheffield Wednesday have sealed the signing of Swedish international attacking midfielder Svante Ingelsson – who has joined from German side Hansa Rostock to become their fourth addition of the summer window.
The 26-year-old follows on from the signings of Max Lowe, Ben Hamer and Yan Valery.
Ingelsson began his career at hometown club Kalmar FF in September 2015 and moved to Italy to join Serie A side Udinese in 2017.
He had a loan spell with Pescara before briefly returning to Kalmar in early 2020 before moving to 2.Bundesliga outfit Rostock in the summer of 2021.
