That is a very interesting video. I’ve estimated the time of the brightest one as 2021-10-11 00:26 and its position as azimuth 177, alt 29. If you search within 2 deg of that for Kelling you get this list of satellites (This is a bit of a mess but I can’t attach a text file since it is not one of the permitted file types:
UTC ID Az Alt Ofs Rg (km) RR (km/s)
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2021-10-11 00:26:00.000000 UTC TOPO 24748 175.99 28.87 1.16 39039.51 -0.070 DIRECTV 6 (TEMPO 2)
2021-10-11 00:26:00.000000 UTC TOPO 32299 175.37 29.43 1.91 38664.80 -0.000 ASTRA 4A (SIRIUS 4)
2021-10-11 00:26:00.000000 UTC TOPO 33414 175.84 28.30 1.50 39268.93 0.004 VENESAT-1
2021-10-11 00:26:00.000000 UTC TOPO 36831 177.75 29.53 1.01 38670.19 0.000 RASCOM QAF 1R
2021-10-11 00:26:00.000000 UTC TOPO 39773 177.53 29.57 0.84 38665.08 -0.001 EUTE 3B
My guess is that the bright one is Eutelsat 3B. It has large solar panels (around 70 m^2) and could certainly flare to negative magnitudes if the geometry was right.