You could use BIMP but you will need the latest v 1.18 for targa input and compile it yourself.
As ofnuts ImageMagick should do it.
Use mogrify and work on copies of the files for saftey. Mogrify can and will overwrite files with the same names. In the folder containing the files. Remember case sensitive *.tga or *.TGA as required.
mogrify -format tga *.TGA
Took ages to find some genuine rle compressed targa files. 12 year old CD from my archive
ImageMagick (mogrify) looks like this.
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tga.jpg [ 90.32 KiB | Viewed 1894 times ]
How to check that they are uncompressed? XnViewMP says they are. The only difference I can see is the Type 2/Type 10 whatever that indicates.
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compare.jpg [ 99.27 KiB | Viewed 1894 times ]