This is not new as the article claims: Passive radars using FM broadcast and 2G GSM were used in the 1990s Yugoslav war.

Yes, a lot of the ideas are not new. Nevertheless, it is currently an active field of research. One of them is "Integrated Sensing and Communication" (ISAC [or ICAS/JC&S/...]).

One idea is to exploit the signal's structure - despite simply trying to correlate the received line-of-sight signal with its delayed copies.

Especially OFDM has a nice structure. You can estimate delays (-> distances) as frequencies along the subcarriers and Doppler shifts (-> velocities) as frequencies along consecutive OFDM symbols. Estimators like maximum likelihood, ESPRIT, MUSIC, and compressed sensing etc. are your friends here for high-resolution results.

Unfortunately OFDM has a problem with large Doppler shifts (velocities). Therefore, people are looking at other multiplexing schemes like OTFS or AFDM.

there's still / again a number of Czech companies in the sector ... the "passive Radar" came from a Czech cold war project (Tamara). Yes it had a spotlight moment when some F-117 were shot down in the Yugoslav war.