I started building a train route in 1.21.1 some weeks ago, and today I made backup and tried 24w33a to try the minecartMaxSpeed function. Before I tried the new function, I found that my stations cannot make minecarts stop. Also, the minecart can travel in reverse direction on my railway at low speeds.

The deactivated powered rail can make a fast minecart go slower, but it can't make it stop. Once a minecart at top speed (default 8 blocks per second) passes one single deactivated powered rail it can get slower. Nevertheless, as soon as it slows, the other deactivated powered rails cannot let it stop. On the other hand, when you press "s" to slow the minecart down then pass deactivated powered rails, THEY MAKE THE MINECART MOVE FASTER!

↑ one of my stations. it looks primitive, but minecarts in 1.21.1 can slow down at the first powered rail and fully stop at the second. In 24w33a minecarts can go through the second one without me pressing "w".

↑ A part of my railway. In 24w33a minecarts can travel upwards on the left route at a low speed.

Hope my advice is useful!