Many wikis (P38161 from T271114) set a minimum thumb width,

/* Minimum thumb width */
figure[typeof~='mw:File/Thumb'],
figure[typeof~='mw:File/Frame'],
.thumbinner {
	min-width: 100px;
}

The discussion at enwiki asks if this is even needed anymore,
https://en.wikipedia.org/wiki/MediaWiki_talk:Common.css#Update_for_T314318

but, if so, maybe the thumbnail feature should provide it by default?

T154077 is an example of a similar upstreaming.