Yes, JEE advanced shall be conducted online, so you can take a good feel of exam by joining mock series by AllenKota which is highly helpful and is quite comprehensive, your approximate ranks are also offered which gives you fair idea on improvement.

You can also get some chapter wise mock tests which is very helpful in below link.

https://www.simplylearnt.com/examination/JEE-Advanced/practice_tests

Some top tips for preparation shared blow:-

https://engineering.careers360.com/articles/jee-advanced-preparation-tips-physics-chemistry-and-mathematics

Make sure you give atleast 20 mock exams and keep analysisng mistakes and focus on weak areas to transform them into strengthgs.

I would suggest you to go through the below provided preparation tips for the same -

1. Know your Syllabus Well.
2. Work on a Time Table.
3. Make your Basic Concepts Strong.
4. Improve your Weak Points.
5. Write Notes and Prepare Flash Cards.
6. Attempt Mock Test and Solve Sample Papers.
7. Revision is must.
8. Make Sure to Take Breaks.
9. Check out Proper Books for Preparation.

Also, to give your best in CBT it would be better if you devote maximum time of yours in online mock test once you are done with your syllabus and sample/previous year papers as this is helpful to get right time management skills and through this you will be able to get to know about the actual test pattern and most importantly when you check the test analysis report properly then it will show where all you are still lacking and where all you have to work really hard and accordingly you can revise the topics.

Hope this helps!!!