Numeric tags should be supported, and the current canonical URL format is intended to avoid this ambiguity.
For example, if the tag is named 2026 and its tag ID is 3, the canonical URL should be:
/tag/2026/3
The ambiguous form is the older/legacy URL:
/tag/2026
That can be interpreted as “tag with ID 2026”, so if another tag has that ID, it may resolve to that other tag instead of the tag named 2026.
Where are you trying to use or access the tag? If the link is generated by Discourse itself, I would expect it to use the canonical /tag/:slug/:id URL. If you are typing the URL manually, using an old saved link, a custom theme/plugin link, or an imported/sidebar/custom URL, it may still be using the ambiguous legacy format and resolve to the wrong tag.