No ads, nor blockings or nasty popups in YT with the inbuild ad/trackerblocker of Vivaldi, but in FF with uBO and also in Vivaldi if i use uBO instead of the inbuild blocker, not so using Adblock Plus, which is somewhat strange.
The filterlists i use in the Vivaldi adblocker are
https://downloads.vivaldi.com/lists/abp/abp-filters-anti-cv-current.txt
https://downloads.vivaldi.com/easylist/easylist-current.txt
https://secure.fanboy.co.nz/fanboy-cookiemonster.txt
https://www.i-dont-care-about-cookies.eu/abp/
Vivaldi trackerblocker lists
https://downloads.vivaldi.com/ddg/tds-v2-current.json
https://downloads.vivaldi.com/easylist/easyprivacy-current.txt
https://raw.githubusercontent.com/AdguardTeam/FiltersRegistry/master/filters/filter_17_TrackParam/filter.txt
https://raw.githubusercontent.com/uBlockOrigin/uAssets/master/filters/resource-abuse.txt
Only extensions (related to privacy) i use are JShelter and SiteBleacher (fingerprints/scripts and sitedata, good complements to any adblocker)