Yes and no. ‘Yes’ because I know you have to root your device to write fonts on the system partition.
‘No’ because other makers let you add community themes with custom fonts on non-rooted devices.
In my previous Honor 8, I tweaked a theme package, I installed it, and my fav font was used by the entire phone (exepts for those apps that embeds their own fonts for branding). The default font was my selection everywhere. To uncover all my cards, this was with Android 8.1, I don’t know it still is with Android 10 and later.
Well, I miss the details here (I’m a coding enthusiast but not a pro) but if they do, it means it possible.
I can take as an answer “I will not do it”. I can’t buy, so far, " it’s unfeasible " as an answer.