Filter: Glaxnimate mask - opacity of mask filling

Hello, I have been working on a “YouTube channel subscription teaser” for quite some time, for which I used the Glaxnimate mask filter. The animation is complicated by the opacity of the fill, whether I choose to cover the surroundings or the object itself. Is it possible to make the fill partially transparent during animation? If I don’t select “fill” in the menu, the animation is created but not masked.
I am attaching a sample of what I have created – the original idea was that the animation would not have a background (here is a PNG image) and I would insert it as an MLT shot in other projects. Thank you for any suggestions, advice, etc. Thank you for this great program and to the whole community. Sample:https://youtu.be/eIGfdr1Wi0I

Maybe I’m missing something, but isn’t it more or less the same question as in this topic?

Change the fill color’s alpha value less than 255