No one has ever reported not being able to select a clip on the timeline.
Below, each clip is first single-clicked in turn. Preview does not respond, and is perhaps why you believe that the clip can't be selected.
Then, each clip is double-clicked, and preview displays each accordingly.
When focus has been shifted away from the timeline, single-clicking will only select a clip; it won't preview until it's double-clicked.
Be aware too that when a video clip is selected, the audio track will not change to to grey if audio and video are not linked, as with clip 3 in the video below.
This is normal behavior. When posting, please profile a brief, descriptive subject.
Record_2020_09_29_13_37_47_724.mp4