What you're talking about is commonly called "curtailment", where power generators like wind and solar can be told to basically stop feeding into the grid, effectively wasting their energy.

From what I recall, curtailment of wind and solar at least in Germany amounts to about 3% wasted energy from those sources, so no, it's not a very significant worry. These renewable sources really are displacing fossil fuels.

A big part of this story is batteries. Especially during the summer, the wholesale electricity price in Germany can swing daily from -10 to +10 cents per kWh during the mid-day, up to 150+ cents per kWh at night, due to supply-and-demand.

This gradient in prices creates a huge incentive for people to build batteries that buy up cheap electricity during the day (sometimes literally getting paid to do so), so that they can sell it back later on in the day when prices rise. This incentive helps make sure energy does not get wasted, it encourages more batteries to be installed, and it encourages businesses to shift the their energy usage to times of the day that align with high renewable output.