Zoom videoconferencing includes the capability to record sessions, either locally or to Zoom's "cloud" storage. Recordings in either place are captured in some internal Zoom format, and then processed into H.264 / .MP4 files after the session ends. By default, the video resolution of the output files is the lowest that Zoom believes they can get away with -- usually an almost-unwatchable 360p for most meetings/webinars that only show who was speaking. In some cases, if one or more of the participants has a HD-resolution webcam, it may come out at 720p and look quite a bit better, but that seems to be luck of the draw. Between speaker-view vs. gallery-view and who on the call happens to have which hardware, there is almost no way to predict how the recordings will come out in the end. Virtual events have had quite a few disappointing results when they try to record panels and sessions and make them available for re-viewing afterward.
However, there is a simple way to force a higher resolution up front, using a mostly-undocumented trick during the session. TL;DR, all that has to be done is a screen-share of content at the desired output resolution, preferably as recording begins. Evidence indicates that if appropriate material is shared at *any* point during the session, the output recording resolution will be forced to that regardless of what participant video inputs looked like. So, what is now advised to groups running virtual events is to begin sessions with an appropriately high-resolution "bumper slide" or title slate, some kind of branded graphic that introduces the session. It is also nice to have that visible as "audience" viewers enter the session, such as when the webinar "goes live" or the people in the meeting waiting-room are let in.
This is loosely referred to in Zoom's article about final recording resolutions, but no specific statement about forcing the desired resolution is made there. Note that whatever material is shared should be displaying in native 1:1 pixel resolution, whether it's an individual app window or an entire screen. All of this is somewhat dependent on the available monitor resolution of whoever is sharing the material. Modern PC-class machines tend to have standard 16:9 HD 1080p displays, so full-screening an image to share generally does the right thing on those. Mac-class machines tend to have a weirder mix of display resolutions. Only the image-viewing app itself should be shared, rather than "entire screen", which tends to produce a cleaner share whether the individual app in question is itself in its own full-screen mode or not. If someone is on a 4K monitor, then only a display window of a 1920 x 1080 graphic is needed. The point is to make Zoom see the full visible resolution of whatever gets shared, and for some murky reason, that governs what the eventual output resolution will be in the recording *after the fact*.
The meeting settings for the Zoom user running the session should also include "enable group HD", which will at the very least allow 720p participant video to resolve correctly within the sessions, for "pro" and up level accounts. This also tends to make livestreamed sessions look better. According to Zoom this does not affect recordings, but Zoom has misled us about function and features in the past.
The tools used to display graphics properly vary all over the map, but generally a local image viewer can be used if it can be run as "frameless" as possible. It is also doable in a browser; see this video from a past event's training material, at about 03:30 in, with the caveat that "full screen" referenced in that really means the maximum 1920 x 1080 full-HD resolution of the particular laptop it was generated on.