I should have some rewards for this month, but none show in rewards tab

Brave Rewards Rewards Support
2

You can try the steps I’ve mentioned at

NOTE
Those steps will work only for Gemini if you were connected to Gemini on this rewards profile earlier. If you were connected to Uphold, this probably won’t work.
If you’re from a region listed at

this might work for Uphold too, but if you were you won’t have greyed out buttons anyway.