Seems to work fine on disco:

sarnold@millbarge:~$ sudo apt install libssl1.1 openssl
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  linux-image-5.0.0-20-generic linux-image-5.0.0-21-generic linux-image-5.0.0-23-generic linux-modules-5.0.0-20-generic linux-modules-5.0.0-21-generic linux-modules-5.0.0-23-generic
  linux-modules-extra-5.0.0-20-generic linux-modules-extra-5.0.0-21-generic linux-modules-extra-5.0.0-23-generic
Use 'sudo apt autoremove' to remove them.
The following packages will be upgraded:
  libssl1.1 openssl
2 upgraded, 0 newly installed, 0 to remove and 23 not upgraded.
Need to get 1,928 kB of archives.
After this operation, 15.4 kB of additional disk space will be used.
Get:1 http://wopr/ubuntu disco-proposed/main amd64 libssl1.1 amd64 1.1.1b-1ubuntu2.4 [1,305 kB]
Get:2 http://wopr/ubuntu disco-proposed/main amd64 openssl amd64 1.1.1b-1ubuntu2.4 [624 kB]
Fetched 1,928 kB in 0s (15.5 MB/s)
Preconfiguring packages ...
(Reading database ... 91100 files and directories currently installed.)
Preparing to unpack .../libssl1.1_1.1.1b-1ubuntu2.4_amd64.deb ...
Unpacking libssl1.1:amd64 (1.1.1b-1ubuntu2.4) over (1.1.1b-1ubuntu2.1) ...
Preparing to unpack .../openssl_1.1.1b-1ubuntu2.4_amd64.deb ...
Unpacking openssl (1.1.1b-1ubuntu2.4) over (1.1.1b-1ubuntu2.1) ...
Setting up libssl1.1:amd64 (1.1.1b-1ubuntu2.4) ...
Setting up openssl (1.1.1b-1ubuntu2.4) ...
Processing triggers for man-db (2.8.5-2) ...
Processing triggers for libc-bin (2.29-0ubuntu2) ...
sarnold@millbarge:~$ sudo apt install libssl1.1=1.1.1b-1ubuntu2.1 openssl=1.1.1b-1ubuntu2.1
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  linux-image-5.0.0-20-generic linux-image-5.0.0-21-generic linux-image-5.0.0-23-generic linux-modules-5.0.0-20-generic linux-modules-5.0.0-21-generic linux-modules-5.0.0-23-generic
  linux-modules-extra-5.0.0-20-generic linux-modules-extra-5.0.0-21-generic linux-modules-extra-5.0.0-23-generic
Use 'sudo apt autoremove' to remove them.
The following packages will be DOWNGRADED:
  libssl1.1 openssl
0 upgraded, 0 newly installed, 2 downgraded, 0 to remove and 23 not upgraded.
Need to get 0 B/1,921 kB of archives.
After this operation, 15.4 kB disk space will be freed.
Do you want to continue? [Y/n] 
Preconfiguring packages ...
dpkg: warning: downgrading libssl1.1:amd64 from 1.1.1b-1ubuntu2.4 to 1.1.1b-1ubuntu2.1
(Reading database ... 91100 files and directories currently installed.)
Preparing to unpack .../libssl1.1_1.1.1b-1ubuntu2.1_amd64.deb ...
Unpacking libssl1.1:amd64 (1.1.1b-1ubuntu2.1) over (1.1.1b-1ubuntu2.4) ...
dpkg: warning: downgrading openssl from 1.1.1b-1ubuntu2.4 to 1.1.1b-1ubuntu2.1
Preparing to unpack .../openssl_1.1.1b-1ubuntu2.1_amd64.deb ...
Unpacking openssl (1.1.1b-1ubuntu2.1) over (1.1.1b-1ubuntu2.4) ...
Setting up libssl1.1:amd64 (1.1.1b-1ubuntu2.1) ...
Setting up openssl (1.1.1b-1ubuntu2.1) ...
Processing triggers for man-db (2.8.5-2) ...
Processing triggers for libc-bin (2.29-0ubuntu2) ...
sarnold@millbarge:~$ sudo apt install libssl1.1 openssl
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  linux-image-5.0.0-20-generic linux-image-5.0.0-21-generic linux-image-5.0.0-23-generic linux-modules-5.0.0-20-generic linux-modules-5.0.0-21-generic linux-modules-5.0.0-23-generic
  linux-modules-extra-5.0.0-20-generic linux-modules-extra-5.0.0-21-generic linux-modules-extra-5.0.0-23-generic
Use 'sudo apt autoremove' to remove them.
The following packages will be upgraded:
  libssl1.1 openssl
2 upgraded, 0 newly installed, 0 to remove and 23 not upgraded.
Need to get 1,928 kB of archives.
After this operation, 15.4 kB of additional disk space will be used.
Get:1 http://wopr/ubuntu disco-proposed/main amd64 libssl1.1 amd64 1.1.1b-1ubuntu2.4 [1,305 kB]
Get:2 http://wopr/ubuntu disco-proposed/main amd64 openssl amd64 1.1.1b-1ubuntu2.4 [624 kB]
Fetched 1,928 kB in 0s (68.3 MB/s)
Preconfiguring packages ...
(Reading database ... 91100 files and directories currently installed.)
Preparing to unpack .../libssl1.1_1.1.1b-1ubuntu2.4_amd64.deb ...
Unpacking libssl1.1:amd64 (1.1.1b-1ubuntu2.4) over (1.1.1b-1ubuntu2.1) ...
Preparing to unpack .../openssl_1.1.1b-1ubuntu2.4_amd64.deb ...
Unpacking openssl (1.1.1b-1ubuntu2.4) over (1.1.1b-1ubuntu2.1) ...
Setting up libssl1.1:amd64 (1.1.1b-1ubuntu2.4) ...
Setting up openssl (1.1.1b-1ubuntu2.4) ...
Processing triggers for man-db (2.8.5-2) ...
Processing triggers for libc-bin (2.29-0ubuntu2) ...