It might be a new bug coming with some latest release of Spring-boot (and then : Spring).
I had it. The workaround is to put in your pom.xml this corrected dependency :
<!-- Pour contourner un bug à la génération par Spring-boot 2.4.x :
Failed to execute goal org.apache.maven.plugins:maven-resources-plugin:3.2.0:resources (default-resources) on project application-etude: Input length = 1 -->
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-resources-plugin</artifactId>
<version>3.1.0</version>
</plugin>
But this is a temporary workaround to ‘save you’ at the time the trouble fall upon you.
The way to correct the trouble correctly is to ensure that your properties files are now correctly encoded in UTF-8.
Because the underlying cause that makes this problem appearing is the presence of “junk chars” replacing accented characters when ISO-8859-1 (or other) properties files are considered as UTF-8 ones by Spring, while they aren’t.