Is there any software update from 10.13.6 to 10.14 possible for IMac 21,5 End 2013?

Viking, thanks for the answer. It needed a bit of time to come so far.

I made the update to Catalina, but now, im not native english, my outlook for 2011 does'nt work anymore because of the 32/64 bit stuff. The time before the update the Mac was slow, but now it is sslloooww.:-). Is Catalina the reason?

Next Question, can i go back to Mojave to have the outlook back again? It is my complete e-mail communication from many years and my back ups do all depend on the same system.

Now, i came to the point to determine on what Volume to install the backup.

I clicked Macintosh HD and was told that i can not install that because HFS cannot be installed to APFS or so.

I'm still with Catalina. It's boring.

Sorry if we had a missmatch.

My fault was to install Catalina on my Mac. So i lost my 2011 Outlook for Mac.

Than i wanted to reinstall Catalina to High Sierra to have access to my e-mails again.

After that i want to update to Mojave to access a program working with 64bits.

I've tried to revert to high sierra again, made a restart and the cmd-R combination does not work.

There's no box to choose "Backup from time machine". Mac starts as usual.

Don't have any. so i can't do with my wireless keyboard?

3rd option is: have a friend...:-).

Now i'm going to try and keep you informed if i hopefully come back.