I use Debian but I expect my research also applies to Ubuntu.
The last version of libapache2-mod-fastcgi in Debian was non-free in Jessie see libapache2-mod-fastcgi (2.4.7~0910052141-1.1+deb8u1) and it was dropped in favor of libapache-mod-fcgid in 2016.
Debian gives a choice of libapache2-mod-fcgid (buster) as a binary-compatible alternative to Apache module mod_fastcgi, or mod_proxy_fcgi in apache2-bin (buster).
I used mod_proxy_fcgi and probably installed it in a similar manner to this post. In my case I created a urbackup.conf file for inclusion in existing virtual servers.
# UrBackup configuration file for apache 2.4 or later
<IfModule mod_alias.c>
Alias /urbackup /usr/share/urbackup/www
</IfModule>
<Directory "/usr/share/urbackup/www">
<IfModule mod_authz_host.c>
Require local
Require ip 172.30.0.0/16
</IfModule>
</Directory>
<IfModule mod_proxy_fcgi.c>
ProxyPass "/urbackup/x" "fcgi://127.0.0.1:55413"
</IfModule>
Check Apache Module mod_proxy for important information on open proxy servers if you make wider use of mod_proxy.
There is an Oracle article Migrating to the mod_proxy_fcgi and mod_authnz_fcgi Modules that seems to give step by step instructions on switching to mod_proxy_fcgi.