It depends on your English level really, and the band score you need. If it's very good, you'll likely be fine. However, usually it's a good idea to get feedback on writing and speaking from someone who knows the test criteria well. You can post writing and speaking here but usually you will get comments from people who don't know the IELTS requirements. For example, they'll correct the grammar and vocabulary mistakes in your writing, but will say nothing about task response and cohesion and coherence. Also, very often, the grammar and vocabulary corrections focus only on accuracy. You don't get comments that improve the range. The usefulness of correction here is very limited for exams with specific marking criteria. Good luck in the test!

There are lots of IELTS resources on the internet. Reading and listening you can study by yourself but you can ask here if you don’t understand why an answer is correct. You can post writing here too and people will help you. Speaking maybe needs a teacher most, but you can post voice notes.

In 2022, according to IELTS's statistics, 19.6% of native English speakers were able to get a Band 8 or above and the average score for native speakers is Band 7. That's because there are many unusual requirements that we do on exam that we don't do in day-to-day conversation. As mentioned by others, an inexperienced, unqualified "IELTS teacher" will usually just correct grammar mistakes and say you have "good pronunciation" without understanding the range of phonology features which should be demonstrated. At the very least, doing a diagnostic with an experienced teacher for your wiring and speaking will, at the very least, point out your strengths and weaknesses as stated in the Band Descriptors.