tl;dr version:
The Workspace Switcher applet currently has somewhat misproportioned dimensions for the individual workspaces' icons. See the screenshots attached; Workspace Switcher on a horizontal panel is on the right hand side of the image.
Extended version:
If placed on a vertical panel, the height of each workspace rectangle is too low. Switching the workspaces using the mouse (not mentioning the touchpad) requires some dexterity. If placed on a horizontal panel, the height of the workspaces' rectangles is too big.
I use currently Ubuntu MATE 21.10 (nice release BTW) and therefore I'm also using MATE 1.26. I also gave a try to the MATE 1.26 already on Ubuntu MATE 20.04 LTS, I used the repository https://launchpad.net/~ubuntu-mate-dev/+archive/ubuntu/fresh-mate to do that. I didn't notice the misproportions of the workspaces' icons there but I eventually may not remember correctly. I am sure these misproportions weren't present on MATE 1.24.
Does anyone have the similar problem? Does anyone know how to fix this eventually please? Also, if anyone knows if/how/where to report this, feel free to use any bit of information I just posted here.