#sudo apt install curl
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following additional packages will be installed:
  libcurl4
The following NEW packages will be installed:
  curl libcurl4
0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
Need to get 608 kB of archives.
After this operation, 1,188 kB of additional disk space will be used.
Do you want to continue? [Y/n] y
Err:1 http://deb.debian.org/debian bullseye/main amd64 libcurl4 amd64 7.74.0-1.3+b1
  404  Not Found [IP: 146.75.94.132 80]
Err:2 http://deb.debian.org/debian bullseye/main amd64 curl amd64 7.74.0-1.3+b1
  404  Not Found [IP: 146.75.94.132 80]
E: Failed to fetch http://deb.debian.org/debian/pool/main/c/curl/libcurl4_7.74.0-1.3%2bb1_amd64.deb  404  Not Found [IP: 146.75.94.132 80]
E: Failed to fetch http://deb.debian.org/debian/pool/main/c/curl/curl_7.74.0-1.3%2bb1_amd64.deb  404  Not Found [IP: 146.75.94.132 80]
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

解决办法：

sudo apt update

再次安装：

sudo apt install curl

已成功解决。上述对我有用的解决方法可能对你不起作用时。在这种情况下，我建议你按顺序运行以下命令来安装可能已卸载的所有丢失的软件包

sudo apt clean
sudo apt update
sudo apt install --fix-missing

还有，你可以简单地运行sudo apt update --fix-missing命令来安装缺少的更新。

sudo apt update --fix-missing