thank you for reaching out to the Wegugees community and for sharing your important question with us.
My name is Christine, I'm a linguist and member of the mbeon-staff.
Of course you can sit any language exam without having attended a course. But I'd strongly recommend you to get acquainted with the test formats.
If you want to take a Telc exam, you will find information and mock-tests here: https://www.telc.net/pruefungsteilnehmende/sprachpruefungen/pruefungen/detail/telc-deutsch-b2.html
For a Goethe exam, please learn more here: https://www.goethe.de/de/spr/kup/prf/prf/gb2.html.
The test of both institions differ visibly, though both require a sound B2-level. Goethe have modularised their exams, there are four parts (reading, writing, listening and speaking) and if fail in one part you have to repeat only this single part, whrereas at Telc you have to repeat the whole wriiten part (that is listening, reading and writing) if you fail in one of these sections. On the other hand telc offers specialised exams like German for work B2 oder B2 nursing or B2/C1 for physicians.
I hope my answers were useful for you and I'll be very pleased if you contact me again with further questions. I'm a member of the mbeon-staff and I‘ll be glad to guide over a longer period of time.
mbeon is an online advisory service for migrants via the mbeon-app, which you can download on your smartphone for free. You'll find me in the mbeon-app under my name München, Frau Müller and get confidential one-to-one advice in a safe virtual room where nobody can read messages. For further information please visit www.mbeon.de.
Download for Android: https://play.google.com/store/apps/details?id=de.zone35.mbeon
Download for iOS: https://apps.apple.com/de/app/mbeon-messengerberatung/id1408795643