The crossing to Vientiane at Nong Khai is open but the last I read you have to enter with a tour group, Check with a travel agency in Udon about it. You need to be fully vaccinated and have a current RT-PCR test. There is info in this topic but it is little out of date since the bridge is open now. https://aseannow.com/topic/1222117-travel-restrictions-and-entry-requirements-for-laos-during-covid-19/?do=findComment&comment=17245569
To return you will need a Thailand Pass and $20,000 of medical certificate.
Not a easy option but better than anything else at this time.