Various things that logged debug messages with CSS_PARSER_DEBUG enabled. Some aren't CSS though.

Non-CSS

• PerformanceEntry event type
• Navigator.maxTouchPoints
• A bunch of parse_as_sizes_attribute() failures

Fonts

• @font-face { font-display }
• text-rendering
• font-synthesis/font-synthesis-weight
• font-feature-settings
• text-size-adjust
• font-variant-numeric
• text-underline-offset
• font-display

Text formatting

• tab-size
• hyphens
• word-break
• text-wrap
• white-space: wrap (text-wrap-mode longhand)

SVG

• <filter>
• <fe*> elements
• <animate>
• stroke-dasharray
• shape-rendering

Containment

• contain and its various longhands
• isolation
• container-type
• @container

Scrolling

• scroll-margin-*
• overscroll-behavior

Motion path

• offset-rotate
• offset-anchor

Transforms

• rotate
• scale
• perspective
• transform-style

Masking

• mask-image
• mask-composite
• -webkit-mask: linear-gradient(270deg,#000 0,#000)
• clip-path: inset(100%)

Misc

• color(display-p3 0.898 0.2824 0.302)
• hsla(,1) - Caused by a bug in cascading variables. Fixed by #1310.
• filter
• resize
• will-change
• border-image / border-image-source
• fit-content in a calc()

Can't find in specs, might be wrong/typos

There were a few genuine typos mixed in which I've not included. Plus a couple of features only one browser ever supported and then removed support for.

• touch-action
• background-clip: none (and -webkit-background-clip: none)
• flex-wrap: none
• align-items: middle
• text-fill-color
• font-weight: medium is not a valid value, according to all browsers. We handle it correctly.