MC Version: 1.18.1
Side:       client
Output:     C:\Users\cvalley\AppData\Roaming\.minecraft\libraries\net\minecraft\client\1.18.1-20211210.034407\client-1.18.1-20211210.034407-mappings.txt
javax.net.ssl.SSLHandshakeException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at java.base/sun.security.ssl.Alert.createSSLException(Alert.java:131)
    at java.base/sun.security.ssl.TransportContext.fatal(TransportContext.java:370)
    at java.base/sun.security.ssl.TransportContext.fatal(TransportContext.java:313)
    at java.base/sun.security.ssl.TransportContext.fatal(TransportContext.java:308)
    at java.base/sun.security.ssl.CertificateMessage$T12CertificateConsumer.checkServerCerts(CertificateMessage.java:654)
    at java.base/sun.security.ssl.CertificateMessage$T12CertificateConsumer.onCertificate(CertificateMessage.java:473)
    at java.base/sun.security.ssl.CertificateMessage$T12CertificateConsumer.consume(CertificateMessage.java:369)
    at java.base/sun.security.ssl.SSLHandshake.consume(SSLHandshake.java:396)
    at java.base/sun.security.ssl.HandshakeContext.dispatch(HandshakeContext.java:480)
    at java.base/sun.security.ssl.HandshakeContext.dispatch(HandshakeContext.java:458)
    at java.base/sun.security.ssl.TransportContext.dispatch(TransportContext.java:200)
    at java.base/sun.security.ssl.SSLTransport.decode(SSLTransport.java:172)
    at java.base/sun.security.ssl.SSLSocketImpl.decode(SSLSocketImpl.java:1500)
    at java.base/sun.security.ssl.SSLSocketImpl.readHandshakeRecord(SSLSocketImpl.java:1415)
    at java.base/sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:450)
    at java.base/sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:421)
    at java.base/sun.net.www.protocol.https.HttpsClient.afterConnect(HttpsClient.java:580)
    at java.base/sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:183)
    at java.base/sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1665)
    at java.base/sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1589)
    at java.base/sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:224)
    at java.base/java.net.URL.openStream(URL.java:1161)
    at net.minecraftforge.installertools.DownloadMojmaps.process(DownloadMojmaps.java:65)
    at net.minecraftforge.installertools.ConsoleTool.main(ConsoleTool.java:55)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at net.minecraftforge.installer.actions.PostProcessors.process(PostProcessors.java:226)
    at net.minecraftforge.installer.actions.ClientInstall.run(ClientInstall.java:144)
    at net.minecraftforge.installer.InstallerPanel.run(InstallerPanel.java:423)
    at net.minecraftforge.installer.SimpleInstaller.launchGui(SimpleInstaller.java:175)
    at net.minecraftforge.installer.SimpleInstaller.main(SimpleInstaller.java:147)
Caused by: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at java.base/sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:439)
    at java.base/sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:306)
    at java.base/sun.security.validator.Validator.validate(Validator.java:264)
    at java.base/sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:231)
    at java.base/sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:132)
    at java.base/sun.security.ssl.CertificateMessage$T12CertificateConsumer.checkServerCerts(CertificateMessage.java:638)
    ... 28 more
Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at java.base/sun.security.provider.certpath.SunCertPathBuilder.build(SunCertPathBuilder.java:141)
    at java.base/sun.security.provider.certpath.SunCertPathBuilder.engineBuild(SunCertPathBuilder.java:126)
    at java.base/java.security.cert.CertPathBuilder.build(CertPathBuilder.java:297)
    at java.base/sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:434)
    ... 33 more
Failed to run processor: javax.net.ssl.SSLHandshakeException:PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
See log for more details.
 

uninstall java completely the reinstall java

It didn't work.All other versions of forge are working fine but only 1.18 cannot be downloaded