经过好几天的不断摸索，找到了 。

机型：DELL lnspiron 3543

系统：Deepin 20.2

无线网卡型号：BCM 43142

问题描述： 搜索不到无线网信号。

解决方案：（亲测，有效。原文来自：https://bbs.deepin.org/en/post/218215）

I solved this problem with WiFi. The error was in the driver. The instructions I have compiled are only suitable for Broadcom owners.

1 step: use command (delete broadcom drivers)

sudo apt remove --purge broadcom-sta*

2 step: download latest version of drivers from Debian Packages (only buster-backports) using this commands: 

wget http://ftp.ru.debian.org/debian/pool/non-free/b/broadcom-sta/broadcom-sta-common_6.30.223.271-15~bpo10+1_all.deb
wget http://ftp.ru.debian.org/debian/pool/non-free/b/broadcom-sta/broadcom-sta-dkms_6.30.223.271-15~bpo10+1_all.deb
wget http://ftp.ru.debian.org/debian/pool/non-free/b/broadcom-sta/broadcom-sta-source_6.30.223.271-15~bpo10+1_all.deb

3 step: install drivers using commands:

sudo dpkg -i broadcom-sta-common_6.30.223.271-15~bpo10+1_all.deb
sudo dpkg -i broadcom-sta-dkms_6.30.223.271-15~bpo10+1_all.deb
sudo dpkg -i broadcom-sta-source_6.30.223.271-15~bpo10+1_all.deb

Complete! Sorry for my English :)

Second problem resolved by command 

sudo apt remove deepin-recovery-plugin

重启一下电脑，就好了。