Lightroom classic tools

Brushes, gradients, etc are now accessed via a button on right side of toolbar under the histogram. I've attached a screenshot that should help you locate the various masking tools.

If you are looking at tutorials for older versions:
FYI the tools bar under the histogram, has recently changed a bit.

The various local adjustment types such as Gradient and Brush are now presented only in a Masks panel that opens up as needed, rather than appearing as separate tools all the time - you can click the rightmost tool icon (circular symbol) to access this new panel. The clone / heal tool has also been given a graphically different icon.