Roku OS can lightly influence the type of ads you end up seeing.
In the case of YouTube, the prefer method to track for choosing ads is by being logged into YouTube. However, YouTube does not require you to login to use it.
If you are using YouTube while not logged in, Roku OS can supply two things that may influence the type of ads that are shown. It can provide meta-data for personalized ads and an advertising identifier to help the channel track Roku between different launches of the YouTube channel.
If you don't want Roku OS to supply personalization meta-data then go to Settings -> Privacy -> Advertising and then uncheck Personalize Ads. If you don't want the Roku advertising identifier provided to YouTube (and other channels) to remain the same then choose Reset advertising identifier.
Aside for those two pieces of information, Roku OS doesn't do anything else to influence the ads. Everything else is up to Alphabet/YouTube. The frequency and exactly which ads are selected are determine by the YouTube service. YouTube also chooses the frequency based on which video you are watching. If you see ads more often on Roku than on a laptop it is likely that is because what video is being played on Roku has a higher rate of ads than what video was selected for playback on the laptop.
My experience has been if you play the *same* video on a laptop, android phone, android tv media device and roku while making sure to *NOT* be logged into YouTube on all the devices then the frequency and type of ads remain similar. I have not been able to reproduce any Roku bias except by playing different videos in which the bias is based on which video is being played, not by the device it is played on.