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.

And for those not in the know, a F1 race is ~305km, and they have do two days of practice plus qualifying in a race weekend using the engines they have (same engine for qualifying as for racing). There's some more detail in this[1] article, where they point out the Mercedes F1 engine did over 3000 miles (~4900km) during pre-season testing without issues (most in race-like conditions).

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-...

F1 regulates the maximum number of engines a season (to 3 currently). So they have to last ~7 races.

Edit: old numbers updated