I noticed the significant difference of slower loading of websites as well with 28.3.0. I have been using 28.1.2 instead, as that version works fine.
1 . Personal PC
2. Windows 10 (OS Build 19045.5555)
3 . and 4.
CPU = Intel(R) Core(TM) i5-2400 CPU @ 3.10GHz
RAM = 12.0 GB DDR3
GPU = NVIDIA GeForce GT 1030
SSD = Samsung SSD 870 EVO 1TB
5 . Yes - Window Defender is enabled
6. Yes - Firewall is enabled
7. Yes it persists when BAS is ran as administrator
8. The sites load mildly faster in run mode than in write, but even run mode is significantly slower when compared with past versions
Hope this helps
Edits: fixed numbering from looking wonky