HTML / XML / JS, low-level validity (cross-cutting)HighVerified
Non-responsive/fixed-width layout
What it is
Not mobile-responsive.
Why it matters
Mobile usability failure under mobile-first indexing.
How to fix it
Implement responsive design.
Impact
Medium-high. Direct.
Evidence
Mobile-friendliness matters (mobile-first). Google Search Central, Mobile-first indexing best practices; Google Search Central, Understanding page experience in Google Search results
Sources