I have a lot of problems with Gradle, especially with multiplatform kotlin. Firstly, I constantly have that

Deprecated Gradle features

thing, and IntelliJ idea shows me a lot of warnings despite it technically compiles. Is there any way to fix all of this?

The deprecation warnings just mean that you cannot use Gradle 7+ unless they are fixed. To see which deprecated features were used, use

--warning-mode all

as advised. If you find the deprecated usages are not in your usage but in some plugin you use, report issues for those plugins if there are none yet. If you want to suppress this warning, use

--warning-mode none

or set the Gradle property

org.gradle.warning.mode

to

none

. Regarding the warnings in IJ, hard to tell without you telling what those warnings are.