[LukasCPH]

Anyway, isn't it unusual to have 20+ km laps at the Worlds? I've always thought 20km was a limit.

Indeed.
There is no limit as such, but laps of 14-21 km are definitely the 'standard' in recent years. And going back further, the 'standard' was even shorter - 12-18 km.

I've looked at the last 40 editions (including the cancelled one in Aigle/Martigny), see the list in the spoiler below.
The average distance of a lap was ~16.3 km (allowing for rounding differences), and only five of those were longer than 20 km (Benidorm 1992 at 21.8 km, Madrid 2005 at 21.2 km, Salzburg 2006 at 21.7 km, Innsbruck 2018 at 23.9 km, and Imola 2020 at 28.9 km). This means that Imola is a huge outlier length-wise.

Spoiler (hover to show)

Year	Venue	Distance
2020	Imola	28.9
2020	Martigny	19.4
2019	Harrogate	14
2018	Innsbruck	23.9
2017	Bergen	19.1
2016	Doha	15
2015	Richmond	16.4
2014	Ponferrada	18.3
2013	Firenze	16.6
2012	Valkenburg	16.2
2011	København	14
2010	Geelong	15.8
2009	Mendrisio	13.3
2008	Varese	17.3
2007	Stuttgart	19
2006	Salzburg	21.7
2005	Madrid	21.2
2004	Verona	15
2003	Hamilton	12.3
2002	Zolder	12.8
2001	Lisboa	12.1
2000	Plouay	14
1999	Verona	16.3
1998	Valkenburg	17.2
1997	Donostia	13.5
1996	Lugano	16.8
1995	Duitama	17.7
1994	Agrigento	13.3
1993	Oslo	18.4
1992	Benidorm	21.8
1991	Stuttgart	15.8
1990	Utsunomiya	14.5
1989	Chambéry	12.1
1988	Ronse	13.7
1987	Villach	12
1986	Colorado Springs	15.4
1985	Montello	14.8
1984	Barcelona	13.5
1983	Altenrhein	14.9
1982	Goodwood	15.2