We have the following two URLs:
https://example.com/%D1%82%D0%B5%D1%81%D1%82
https://example.com/%d1%82%d0%b5%d1%81%d1%82
Both are identical except the the case (upper vs lower). Will Google consider them to be duplicate URLs or it does not matter?
<link rel="canonical" href="https://example.com/тест">
then it's not only clear to search engines which version to index, it's clear to human visitors/searchers what you're actually serving.