I'm experiencing a similar issue with template version 2.2 in Unity version 2020.3.31.f1.
It looks like Unity isn't replacing any of the %UNIY_WIDTH% etc placeholders, leading to syntax errors when parsing the resulting html.
Viewing post in (Unity) Better Minimal WebGL Template comments
Are you sure you downloaded the right version of the template? The placeholder strings in v2.2 are in the format "{{{ VARIABLE }}}" instead of "%VARIABLE%"; the latter is the format from v1.1, so you may have accidentally used that instead.
I just double checked template v2.2 against Unity v2020.3.30f1 locally and it seems to work fine, lmk if you have any other issues.
Yes, you're right. I'm not sure how I ended up with an old version. I replaced the files while the editor was open so maybe Unity was running off an in-memory cache rather than the files on disc? Very strange. After replacing with template version 2.2 and verifying the version was correct before launching the editor, it's working much better now. Thank you!