The new rules set the limit at 3 engines per season, which is 21 races plus testing. So it's a balancing act, but you definitely need to reuse the engine for more than 1 race.
That said, from my impression it is usually the turbo or the hybrid systems that break down, it's rare for the actual engine block to be the issue barring specific production issues.
[1]: https://autoweek.com/article/formula-one/mercedes-f1-engine-...