Yeah! If one fails in 10+2, then he/she can apply for the Diploma course with the eligibility conditions of 10th where they will be considered to have 10th as the highest education qualification.

For Diploma in Engineering courses which you can pursue after your 10th & 12th, click the link provided below:

https://engineering.careers360.com/articles/diploma-in-engineering

I hope this helps. Wish you a great day!