I am having the same problem. When I try to login, the loading bar gets as far as "connecting to region" and then SL crashes to desktop. Here are my system specs. This situation is now 5 days old
Second Life Release 6.4.9.549455 (64bit)
Release Notes
CPU: Intel(R) Core(TM) i7 CPU 960 @ 3.20GHz (3207.27 MHz)
Memory: 12280 MB
OS Version: Microsoft Windows 10 64-bit (Build 19041.508)
Graphics Card Vendor: NVIDIA Corporation
Graphics Card: GeForce GTX 970/PCIe/SSE2
Windows Graphics Driver Version: 27.21.14.5206
OpenGL Version: 4.6.0 NVIDIA 452.06
Window size: 2560x1361
Font Size Adjustment: 96pt
UI Scaling: 1
Draw distance: 136m
Bandwidth: 10000kbit/s
LOD factor: 2
Render quality: 6
Advanced Lighting Model: Enabled
Texture memory: 512MB
VFS (cache) creation time: December 06 2018 19:16:38
J2C Decoder Version: KDU v7.10.4
Audio Driver Version: FMOD Studio 2.00.07
Dullahan: 1.7.0.202006241556
CEF: 81.3.10+gb223419+chromium-81.0.4044.138
Chromium: 81.0.4044.138
LibVLC Version: 2.2.8
Voice Server Version: Not Connected
September 30 2020 03:41:44