I just need pronunciation or transcription of this word.

Even YouTube couldn’t find the pronunciation. I recommend you find any of the latest translations by Улий🐝 here on Lingvo and ask him in the comment section. Perhaps, he will help.

..and you should provide him the snippet for clarity: “Having come to the land of Sigerberht, the righteous king, You preached the kingdom of Christ our God...”

Thanks.

So, did Uly help you?

I haven't asked him yet. But I found this which is quite weird.
https://www.howtopronounce.com/sigerberht/

Yes, rather strange...

That sounds weird because it’s just a text to speech “machine” that reads anything the way it sees it. This name is actually spelled Sigeberht and is pronounced [SEE-guh-brt] - it rhymes with “feed a bird”

Thank you very much, Uly!
Would this transcription be correct?
/ˈsiː.gə.bə(r)t/

Yes

Thanks.

Hello Uly! What do you think about this version of pronunciation? Is it the same name?
https://youtu.be/t4HmUnOt2aI

Hi Dimitry! That’s actually a recording of a French name with the French pronunciation. Sigeberht is an Anglo-Saxon name with its own pronunciation.

Okay. Thanks a lot!

No problem)))