Hi,
I have had the same issue and checked different LO-versions.
The culprit isn`t Libre Office!
I jumped back to my siduction-image from the beginning of this year and checked it.
LO is running fine with cpu 3-5%.
I don`t know which update the culprit is, cause too many packages are updated since first of january.
I switched my repo to buster, doing an update and LO is running as expected.
Maybe someone of you have enough time to check it.
I am doing every two weeks an image of my siduction, to jump back, if something happened like this.
see you