I have been earning interest on stablecoins for some time, and I would like to change my strategy. Most stablecoins are pegged to the USD, and with the massive money-printing, I see that to the results of compounding I will need to subtract a big amount due to the actual devaluation of the currency. The amount I can be earning is relative if the currency is also changing value. In the end, I no longer see that much added value of having USD-pegged stablecoins instead of USD.
You are correct here. What I can suggest, sell the stablecoins to get USD when you get a chance. In other words, dont use stablecoins just because they give interest on what you store. When you sell bitcoins, convert to USD/fiat while the bitcoin price is higher and hold that USD/fiat till bitcoin drops and use that to buy back BTC. That is the cycle you must follow, not the intermediary of using a Stablecoin.
Point is that the stable coins had been started to sneakily taking people's money into lending pools and all with no guarantee on the safety and legal concerns. You are defenitely at risk when using them, Tether itself has a lot of controversies - only time will tell how much is legal and correct in their reserve.
Instead, I would like to use crypto coins (not stablecoins) and earn interest on them, without having to worry about any fiat currency they may be pegged to. I am not really searching for a big growth in the currency itself (a new Bitcoin not really what I am looking for now), but instead something of relatively low volatility, to earn interest and on which I can rely that it's not going to underperform fiat currency as exchange.
There is no such cryptocurrency that mines away money while you sleep.

Only methods of growing your money while giving it a low risk of loss, is to deposit the coins on some legit business that is allowing passive income for its investors. Be careful of HYIPs/MLM schemes - those are scam.
Probably the only legit one is investing in a casino bankroll, IMO. But that too the ROI is small and that you have to hand over the money to another company. Currently I dont know which casino is allowing this, previously I have used cryptogames but they have removed this now.