Try a restart.
Check with Unity about this installer and its installation requirements, as a starting point.
Some related discussions:
https://answers.unity.com/questions/1676587/unity-installer-installer-cant-install-unity3d-on.html
https://stackoverflow.com/questions/59237899/unable-to-install-any-unity-version-from-unity-hub
If this is any installer from any vendor and not solely Unity, then there’s potentially a corruption of some sort here, or maybe a hardware failure, or some add-on software is severely tangled.
First, have a complete and current backup, on the off chance this problem is getting worse.
If you can get EtreCheck downloaded and running, then share the report to the clipboard, and then open a new reply here and press the Additional Text button to get a text input box big enough to paste the hardware and software configuration report here, and paste and post it here.