Well, off the top of my head...
Denver, Houston, Washington, Carolina, New Orleans, Detroit, Pittsburgh. Those seven teams don't have anything even remotely resembling a franchise QB on their roster, nor do they really have the means to think they'll get one anytime soon, so those teams would have blank checkbooks open for Lamar 10 seconds after he was even vaguely discussed as being "available".
And that's just seven teams. Then there's the teams that kind of have QBs, but would gladly take the opportunity to look for upgrades if they could. That list includes Miami, Las Vegas, Cleveland, NY Giants, Philadelphia, Atlanta, and Minnesota. And I'm probably shortening this list more than I should.
That's at least 13 teams that I see that would show immediate interest.
And he's better than a lot of teams QBs that they have (like Wentz, Tannehill, etc.), it's just a question of whether those teams would go after him or could afford to do so. Then you also bring in teams like the Jets, 49ers, Bears, etc., who recently drafted young QBs, but I think would be super fine moving them for a guy like Lamar without hestitation.
Basically half the league is the floor to me.
The only teams I would say that wouldn't show interest:
New England, Buffalo, Cincinnati, Jacksonville, LA Chargers, Kansas City, Dallas, Tampa, Green Bay, Arizona, Seattle and LA Rams.
i mean idk that new england or jacksonville would turn down lamar either
mac jones's ceiling is much lower than most other potential franchise QBs and josh mcdaniels and BB were notably fans of lamar in that class and trevor lawrence hasn't shown anywhere close to enough yet that you would turn down an opportunity at lamar if he was available (especially given that he's a florida boy)
also don't think the Rams would turn down that opportunity either - Stafford's been a massive upgrade over Goff but we're now starting to see his limitations somewhat even with talent around him now
so for me it's probably only Bills, Chiefs, Chargers, Bengals, Cowboys, Cardinals, Packers, Bucs
which leaves exactly 2/3 of the NFL and I'm not sure there's a QB that would have more of the NFL after them as a hypothetical free agent other than maybe Mahomes