Embrace Autism is a site with a wealth of information about autism and AuDHD (a combination of autism and ADHD). Most of the clients in my office that suspect they are autistic have been great at masking and operating with a level of functioning that has kept them afloat, but they still feel like something could be amiss. The specific tests that I recommend for learning about whether or not you should consider an autism diagnosis are the RAADS-R, which can be helpful identifying folks that might otherwise escape diagnosis because there traits and behaviors are subclinical, and the CAT-Q, which can also help identify individuals that might be missed because of high masking.
While these tests do not qualify someone to have an autism diagnosis alone, they can be a tool to guide individuals to seek formal diagnosis, should they choose to do so. Formal diagnosis is not necessary in all cases, unless you want to seek accommodations in a workplace or school setting. Sometimes learning about diagnosis can be a relief to people to know they are not alone and that their traits and behaviors they have engaged in for a lifetime have more context.