When you first start out, players are taught to move the back foot backwards for forehands. (This would be the right foot for righties, the left for lefties.) This makes it easy to backswing and opens up a larger hitting zone from the side. Historically, this is how forehands were taught. However, as the game got faster and faster, at higher levels there simply wasn't time to bring the foot back while staying close to the table. This meant that those who did bring the foot back were often forced to step back in a fast rally, putting them at a disadvantage against a player with a quicker forehand stroke, who would now dominate over the table.
And how did that player get that quicker forehand stroke? By not moving the back foot backwards in fast rallies, i.e. there's no back foot, the feet stay parallel to the incoming ball for both forehands and backhands when taken near the table. (When you have more time or are forced off the table, then the foot usually goes back.)
As you improve, experiment with playing forehands with the feet parallel to the incoming ball, or closer to that than you normally do. This allows the quicker stroke. However, you need to be a bit limber to do this - you might need to do some physical training - so not everyone can do this effectively. (I can do it, but not very well - either because I learned early on to always bring my foot back, or because I'm older and no longer train. I always bring my foot backwards for forehands except when blocking.)
In general, if the ball is coming at you slow or if you are off the table, bring the foot back. If you are closer to the table or rushed, keep the feet more parallel. Add that to your Fact Book - which is just an anagram of Back Foot!
Here is an example (8 sec), with 14-year-old Stanley Hsu (far side, about 2400, who just swept the Under 15 Boy’s Singles, Doubles, and Mixed Doubles at the 2023 Nationals) with Coach Cheng Yinghua. Stanley blocks two, and then counterloops close to the table for a winning shot - and does so with his feet parallel to the incoming ball. If he'd tried to bring his right foot back, it would have slowed him down, making the shot more difficult and probably rushed.