I installed the 6.0.90 rc1 Version because I had problems to run Octave 5.2.0 on Big Sur too.
What I noticed is, that after working with octave the fan got louder and louder and my CPU percent of octave was 99%.
I have MacBook Pro (16 Zoll, 2019)
2,6 GHz 6-Core Intel Core i7
6 GB 2667 MHz DDR4
Intel UHD Graphics 630 1536 MB