I had similar issue with gnome. Even after setting transparency, it would lag somewhat. I ended up switching to KDE, which does it well. Though I believe there may be another way with gnome, just not exactly sure. However, I have heard about a theme that might give you what your looking for (haven't tried it) called Nord , you might also need to install the 'gnome tweak tool'
I hope it helps ; Also I have no clue if this will also apply to the terminal.
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