You are missing the recomended JDK. Install the recomended version using Unity Hub

Ive installed Unity 2020.3.18f1 with Unity Hub(3.0.0-beta.4 (while running unity hub as an adiministrator)
and i still get that error saying i dont have JDK, is there any way if downloading the JDK manually, if so can you provide a link?

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Yes you can download the jdk manually

but it is recommended to use the correct jdk version for the specifiq unity version (but I have never encounter any issues using the same jdk version across multiple unity versions)

Also, before downloading, make sure in the preferences tab > external tools > jdk installed with unity

is ticked, and if it doesnt work, uncheck it and set the path manually