does anyone know a hosting service that allows installing 3rd party SSL certificate (Comodo) FOR FREE, WITHOUT buying overpriced 70$/year additional dedicated IP?

(hosters I list are in the Europe / Germany region, please keep that in mind)

Not sure if I understand correctly: you have a SSL-Certificate from Comodo you'd like to use?

In this case https://hosteurope.de/WebHosting/ should work.

Edit: at hetzner you also upload custom SSL-Certs

But if you want a provider that gives you a Lets-Encrypt certificate I would recommend to go with https://www.hetzner.de/webhosting (germany)

Let’s Encrypt certificates are free and supported on many shared hosting providers.

Go for Let's encrypt certificate, or get a VPS if you want to use a custom one.

Shared hosting never got good support for SSL, mainly because SSL was rather "optional" until about 2010, and then focus shifted from shared hosting to virtualisation.

Mydevil.net accepts 3rd party certificates without buying separate IP. They provide easy way to establish Let's Encrypt certs with ease.