This app was mentioned in 2 comments, with an average of 1.00 upvote
I'll 2nd acloud.guru for test cramming, recommend linuxacademy.com for deep dive understanding (30hrs worth of content + labs vs. 8hrs at acloud).
And for drilling practice questions, get this app: https://play.google.com/store/apps/details?id=com.ionicframework.awsArch
The acloud.guru app is out of date, from what I understand. If you drill questions with this app until you can answer 100% to every section and practice test every time, you'll almost certainly pass the exam.
I like ACloud.guru for the exam prep, as there's ~8 hours of material there. I skipped their android app due to cost ($20!) and poor reviews. Found this one: https://play.google.com/store/apps/details?id=com.ionicframework.awsArch
...which is higher rated and only costs $6. Seems really good so far. Huge variety of questions arranged by topic, as well as a warm up and two practice exams. I intend to practice with the app until I can ace each one easily, then I'll schedule my exam.
Linux Academy has over 40 hours of content for the Solutions Architect alone, as well as a TON of other content (from Red Hat certs to Devops to Python and SQL), and it's all included in the same subscription. It has lots of labs and seems very in-depth and comprehensive, so I intend to maintain my membership there and use it to learn as much as I can. After I get my AWS certs, I may do their Red Hat Engineer certification course just to fill in gaps in my knowledge and add another valuable cert to my resume.