It might be possible to retrieve/monitor data on transfer sizes (deposits and withdrawals) in labelled exchange wallets to gauge retail activity. Trading data based on size may be inaccurate given small transfers can be done at high frequency by whales, though accuracy could be improved by filtering by total wallet volume and balance size. These are all just ideas and would be valuable data but might require some work to get (especially since there are so many chains to monitor and get data from now).

Have you tried to see what data you can get from there? You'd probably need a paid plan to get meaningful on-chain data, but they're good.

There is some off-chain data that can give ideas on sentiment (like social media and google trends) though they're just to get an idea of sentiment.