Trying to switch between two pairs of boots enchanted with Soul Speed even without moving on the soul blocks will make them both lose durability or even break them.
Also, by standing on soul blocks, if trying to put on then take off a pair of boots enchanted with Soul Speed again and again, it will lose durability. 
Sometimes, if you have two identical pairs of boots both enchanted with Soul Speed, but different durability, continuously switching them on soul blocks can also make both of them lose durability. 

Steps to reproduce:

1. Obtain and equip a pair of boots enchanted with Soul Speed using the command:

   /give @s netherite_boots[enchantments={"soul_speed": 3}]

2. Stand on a single block of soul soil or soul sand, switch to survival mode, then put on and take off the boots you are currently wearing again and again until you find out that your boots has lost the durability

or

1. Obtain 2 pairs of boots enchanted with Soul Speed using the command:

   /give @s netherite_boots[enchantments={"soul_speed": 3}] 2

2. Stand on a single block of soul soil or soul sand, switch to survival mode, then put on and take off 1 pair of boots again and again until you find out that they have lost durability
3. Switch between the two pairs of boots continuously until you find that both of your pairs have lost some durability. 

or

1. Obtain 2 pairs of different boots both enchanted with Soul Speed and equip one of them
2. Stand on a single block of soul soil or soul sand and then switch to survival mode
3. Continuously switch between the pairs of boots until you find that both of them have lost some durability. 

Note:
According to the mechanism of Soul Speed, only when players walking on soul sand or soul soil with boots enchanted with Soul Speed can it lose its durability. However, the fact is that even when players just simply stand on them with boots enchanted with Soul Speed or simply put them on and off continuously, it can cost durability, which is not intended behavior.

P.S.: Since my laptop does not work well when I record the video, it is bad to attach a video with low FPS.