That is a really old python plugin bevel2_1.py
It is not 100% compatible with Gimp 2.10 but you can get it to work with a bit of user intervention.
Unpack the attached zip. Put bevel2_1.py in your Gimp plugins folder
C:\Users\"yourname"\AppData\Roaming\GIMP\2.10\plug-ins
It works with selections, so use the colour select and select just the text in the text layer.
The plugin is in
Filters -> Distorts -> Bevel
Run the plugin, enter the values.
This is where it breaks in Gimp 2.10 Change the layer mode to Hard Light.
example:
https://i.imgur.com/tztk860.mp4
Suggestion: Avoid these old tutorials
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A better bet for an easy bevel effect in Gimp 2.10 is gt-bevel
Also in the zip is gt-bevel-210.scm put this in
C:\Users\"yourname"\AppData\Roaming\GIMP\2.10\scripts
Find that in
Filters -> Decor -> GT Bevel Choose the 'Curved' option.
example:
https://i.imgur.com/YQuv9sw.mp4