Reaching out for some advice, would greatly appreciate any help

I'm a US (dual) citizen living in the UK with my British retired husband and we'd like to move back to the states this year. I currently work for a US contractor here so would like to submit the I-130 petition for an immigrant visa but not sure if I'm able to do it online from here now that the London US Embassy closed their doors to petitions back in 2020?
The USCIS site states I can submit the petition online but does that only mean if I'm currently residing in the US or can I begin the process here? I understand there's a medical and interview portion he would have to complete so wondering if he has to go stateside for this or if it can be completed here in the UK?
If we're not able to begin this process until I'm stateside, would applying for a K-3 visa make more sense so he can reside with me for up to 2yrs while we petition for the immigrant visa? Appreciate your help as I'm unable to find these answers anywhere! Thanks!
Regards, Delilah